Silent and Failsafe Overflow System

[TJ_Mac]

Hello everybody. First I would like to thank you all for the wealth of information in this thread. I've gotten most of the way through it and understand the basic principles of how this system works. The problem that I am having trouble grasping is how to size the overflow.

I'm going to be building this for a 75g standard 48 X 18 X 21. I am going to be using 1.5" SCH 80 bulkheads and 1.5 SCH40 pipes all the way around. I want to use an external overflow and a 36 X 1 X 4 internal weir to allow for room for returns on either side, although I could be persuaded otherwise.

Laying out the pipe it seems that a comfortable width for the external box would be 26" and 5" depth. What I can't figure out is the height of the box and the size of the holes that I should drill between the tank and the external box. Would I be ok to make 3 holes using the same 64mm drill as I'm using for the bulkheads? Or should I use a smaller drill and make more holes? I am assuming that the size of these holes will effect the height of the box.

I hope I provided enough information, and that it isn't too confusing. If anyone can point me in the right direction it would be much appreciated.

 

[uncleof6]

This is posted in this thread a couple of times already, but I can't find it. It shows an "idealized" pass through for an internal/external on a 48" tank, with full length setup.



I don't think that your flow rate ~ 750 - 800 gph max, justifies the use of 1.5" bulkheads, 1" bulkheads, as in the original design will be more than adequate. Schedule 80 bulkheads are never justified, as black ABS bulkheads are fine; they are optional however, but have a smaller inside diameter.

 

[TJ_Mac]

Thank you very much. I remember seeing that in the thread somewhere, but I couldn't find it either! I went with the 1.5" bulkheads because I figured that since I was running 1.5" pipe I wasn't going to be saving any space by using smaller bulkheads, but I may rethink that. And also because I could find 1.5" sanitary tees but not 1". I was also just going to make the external just big enough to fit the pipes in, but I suppose it does make more sense overall to run it c2c.

 

[uncleof6]

Thank you very much. I remember seeing that in the thread somewhere, but I couldn't find it either! I went with the 1.5" bulkheads because I figured that since I was running 1.5" pipe I wasn't going to be saving any space by using smaller bulkheads, but I may rethink that. And also because I could find 1.5" sanitary tees but not 1". I was also just going to make the external just big enough to fit the pipes in, but I suppose it does make more sense overall to run it c2c.

By all means use the 1.5" pipe and parts, just use 1" bulkheads. Inside use 1.25," outside 1.5" as you wish. Charlotte Pipe and Foundry makes 1.25" sanitary tees, you might have to hunt them down though. But the use of sanitary tees is not "mandatory," just make for less turbulence in the line.

I am thinking two things. The hole size to pane width deal (holes too close to the edge of the glass) and I am thinking on the possibility that the bulkhead size could have a part in some starting issues with lower flow systems, getting back to the "works as designed," and larger bulkheads skewing the system to the higher end.

 

[TJ_Mac]

Ah, I didn't think about the bulkheads making it difficult to start the siphon. I think I will switch to 1" then. I had just remembered Bean saying that the 1" was all he had so went with that.

Now I already have a 2.5" drill. Will it be ok to use that instead of the 2 3/8" in the prints that you posted and readjust the spacing?

 

[uncleof6]

It is just a hypothesis, (insufficient empirical evidence,) about the bulkhead size, based on some anecdotal information concerning large bulkhead/low flow scenarios. It has come up more than once. "As designed" circumvents the question.

Just adjust the spacing, the 1/16th inch lower, and 1/8th inch larger hole is not going to make any difference.

 

[ibscott]

Can someone explain to me the reason for the curved pipes at the top of the overflows? They take up a lot of room in an internal overflow and I'm wondering if 3 straight pipes would be just as effective. What do you gain with the curved tops to the standpipes?

 

[eagle9252]

9.5 is too small. i have a 120 with a 55gal sump and the flow was too slow. i was about to have to add a nano power head in the sump to add some circulation as it was slow moving. but i had 1" return and 1-1/2 drains. i have since went to an external pump with more flow and a 75g sump... much better

Is there a way to estimate my gph with this system or is it more just take a good guess and tune the valves as needed?

I am trying to decide if I want to use my mag 9.5 as the sump return or if I need to get something bigger? Either way it will be used externally and Im going to be running a 48 inch semi coast to coast on a 150 gal long tank with the standard 1 inch bulk to 1.5 pipe.

 

[eagle9252]

I did a small internal overflow with an external overflow to get most of the room inside of the tank. I used 3 bulkheads to allow the flow from the internal to the external overflow.

The main reason for both overflows was to allow room in the tank and still have the coast to coast skimming. but after all this work the other have said it was too big where she wanted it to go...urgh...

Here it is all hooked up. The sump in this picture is a 10g tank. It’s really too small if you want to add filer socks or a fuge or live rock in the sump.

 

[cheezischrist]

ive got a 6ft 125, but am having issues getting that large of glass to go coast to coast. i do have 40" glass though, so can i seam that together and put sorta low brace/baffles on the pieces, or just use the 40" length and close the ends of te box in, and if i dp that, should i make the box deeper for more water volume?

 

[Chris2223]

Hi I am setting up a standard 75g with an external overflow box and understand how the setup works. My only question is, on the external box how tall should it be? My plastic trim is abt 1 3/4" tall, so would I place the external box snug against the bottom of the trim? I am going to drill 4 holes for the water to pass thru with a 45mm ( 1" bulkhead bit) 3 3/4" centered from the top of the glass. Going to space holes 7.5" apart centered. My external box will be 36" long x 4-5" wide. Thanks for your help!

 

[SkyReef]

Using Internal/External Overflow Boxes, How Big Should Pass-Through Holes Be?

Using Internal/External Overflow Boxes, How Big Should Pass-Through Holes Be?

I am doing a BeanAnimal design on a 75-gallon tank, above a 25-gallon-net-quantity sump. I'll be using an internal and external overflow box, with the internal box being very skinny, to save room inside the tank. The holes drilled at the back of the tank will pass water through to the external overflow box, but these pass-through holes will not have bulkheads--just holes in the glass (unless you all recommend against that and recommend using bulkheads at the pass-through holes).

Several Questions:

(1) Re Sump Flow: Is it okay to go with a 5x-per-hour, sump-turnover rate, with much more turnover flow occurring inside the display-tank, supplied by powerheads? If so, the sump-flow-turnover calculation would be: (75g (tank) + 25g (sump)) x 5 = 500 GPH? That may be right, but it just sounds low for a 75 gallon tank. What do you think?

(2) Re Drainline Sizing Overkill: Assuming only 500 gph turnover here, am I going too big by use of 1.5" drain lines on the BeanAnimal Design? I've read that the maximum, vertical flow of the open drain line (water + air) would be about 600 gph, and the siphon drain line, many times that flow rate. So, achieving a 500 gph turnover would require dialing back both the siphon drainline and the open-channel drainline. However, BeanAnimal has recommended the 1.5" open-channel line to assure that no gurgling occurs, which might occur with a smaller diameter line, like a 1.0" line. Thus, while the 1.5" drain lines might be overkill for a turnover of merely 500 gph, I have designed it that way. Yes? No? Maybe so? What do you think?

(3) Re Pass-Through Holes Size and Quantity: Using the internal, coast-to-coast design, I intend to make the internal overflow box merely 1.0" deep (front to back), from which the water will pour into an external overflow box, through holes drilled through the back wall of the aquarium. But here's the question: how many pass-through holes, and how big should they be? I read in two other articles discussing this that three, one-inch holes that feed 1.5" drainlines attached to the bottom of the external overflow box, in a BeanAnimal design, should work fine. However, as I have mocked it up in a drawing, that seems insufficient. It seems as if there should be at least four one-inch, pass-through holes on the back wall feeding into the external overflow box, not three.

Check out these two drawings to get a sense of how small the 1" holes seem, compared to the 1.5" drainlines that are rapidly evacuating water out of the external overflow box. I'm not sure what flow rates are implicated in horizontal, pass-through holes at the back wall of the aquarium--they may be less than vertical holes, where 1.0" holes produce 600 gph. I can't imagine it's going to flow that much through the three pass-through holes.

My big concern: only 3 holes on the back aquarium wall will be insufficient to match the evacuation rate of water through the 1.5" siphon line + 1.5" open channel line. Here are the drawings. What do you think? Should I go with more than three pass-through holes on the back wall of the aquarium? Should they be larger? How many, and how large?

Thanks very much.

 

[uncleof6]

I am doing a BeanAnimal design on a 75-gallon tank, above a 25-gallon-net-quantity sump. I'll be using an internal and external overflow box, with the internal box being very skinny, to save room inside the tank. The holes drilled at the back of the tank will pass water through to the external overflow box, but these pass-through holes will not have bulkheads--just holes in the glass (unless you all recommend against that and recommend using bulkheads at the pass-through holes).

I think running things that tight is going over board. (1" front to back) You are not really saving anything useful by making it that small, and deeper (front to back) would be less likely to cause an issue with flow rate.

Several Questions:

(1) Re Sump Flow: Is it okay to go with a 5x-per-hour, sump-turnover rate, with much more turnover flow occurring inside the display-tank, supplied by powerheads? If so, the sump-flow-turnover calculation would be: (75g (tank) + 25g (sump)) x 5 = 500 GPH? That may be right, but it just sounds low for a 75 gallon tank. What do you think?

This is often recommended, however, I recommend higher ~ 10x.

(2) Re Drainline Sizing Overkill: Assuming only 500 gph turnover here, am I going too big by use of 1.5" drain lines on the BeanAnimal Design? I've read that the maximum, vertical flow of the open drain line (water + air) would be about 600 gph, and the siphon drain line, many times that flow rate. So, achieving a 500 gph turnover would require dialing back both the siphon drainline and the open-channel drainline. However, BeanAnimal has recommended the 1.5" open-channel line to assure that no gurgling occurs, which might occur with a smaller diameter line, like a 1.0" line. Thus, while the 1.5" drain lines might be overkill for a turnover of merely 500 gph, I have designed it that way. Yes? No? Maybe so? What do you think?

The original design, used 1" bulkheads, with 1.5" pipe. Build it like that, and you will have a very wide bandwidth. Capable of more than you will flow in this tank assuming a max 750 gph, which will probably be your water volume, after everything is tossed in the tank, and sump should only run around half full... 12.5 gallons. And possibly a "not quite linked yet" issue with low flow rates and large pipe, may be avoided, using 1" bulkheads. The original design works as intended.

(3) Re Pass-Through Holes Size and Quantity: Using the internal, coast-to-coast design, I intend to make the internal overflow box merely 1.0" deep (front to back), from which the water will pour into an external overflow box, through holes drilled through the back wall of the aquarium. But here's the question: how many pass-through holes, and how big should they be? I read in two other articles discussing this that three, one-inch holes that feed 1.5" drainlines attached to the bottom of the external overflow box, in a BeanAnimal design, should work fine. However, as I have mocked it up in a drawing, that seems insufficient. It seems as if there should be at least four one-inch, pass-through holes on the back wall feeding into the external overflow box, not three.

I would make them as large as practical, for maximum "communication" between the internal and external boxes, and the less noise--1" is really too small, IMHO. The waterline should be around the center line of the holes, so you can see how limiting 1" holes are going to be. Number is an obscure question, and we are not dealing with a gravity/head pressure thing, rather flow through a culvert....I believe that more within reason, is better.

Check out these two drawings to get a sense of how small the 1" holes seem, compared to the 1.5" drainlines that are rapidly evacuating water out of the external overflow box. I'm not sure what flow rates are implicated in horizontal, pass-through holes at the back wall of the aquarium--they may be less than vertical holes, where 1.0" holes produce 600 gph. I can't imagine it's going to flow that much through the three pass-through holes.

My big concern: only 3 holes on the back aquarium wall will be insufficient to match the evacuation rate of water through the 1.5" siphon line + 1.5" open channel line. Here are the drawings. What do you think? Should I go with more than three pass-through holes on the back wall of the aquarium? Should they be larger? How many, and how large?

Thanks very much.

 

[bigfoot610]

just a word of advice if you cant find a particualr fitting at lowes or home depot try an irrigation supply house thye have all kinds of stuff you dont find at depot or lowes

spears will have just about any fitting imaginable http://63.156.201.111/smcweb/EINM021.pgm#

 

[budster.stig1]

Question for Uncleof6

Question for Uncleof6

I have finished my build and waiting for Rock to start cycling, because I used a 1" pipe, bulkhead and elbow for my syphon, and my open channel and emergency are 1 1/2" pipe, bulkhead and elbows, I have limited my flow rate at about 1000gph. My DT is 200g and I would like to increase flow a little. My question is when I increase my syphon, should I jump to 1 1/2" or 1 1/4" pipe, I obviously can not change the bulkhead. How much increased capacity will 1 1/4" provide, I am not looking for 10x flow, just a little more than 5x. Budster:bum:

 

[SkyReef]

[Regarding the internal overflow box being only 1" deep (front to back), uncleof6 writes:]

I think running things that tight is going over board. (1" front to back) You are not really saving anything useful by making it that small, and deeper (front to back) would be less likely to cause an issue with flow rate.

Thanks, Uncleof6. As always, your recommendations are very thorough, detailed, and most helpful.

If I understand you correctly, the 1-inch deep (front to back) internal overflow might cause an issue with flow rate because there is not enough of a volume of water in the skinny internal overflow to keep up with the external box, which is much deeper (front to back). Is that correct? What do you think about a deeper setback (front to back) of 2 inches. Would that be sufficient?

[Regarding a sump turnover rate of 5x per hour, uncleof6 writes:]

This is often recommended, however, I recommend higher ~ 10x.

Higher sounds better, I agree. Are you saying that you recommend ~ 10x turnover through the sump, PLUS additional, turnover inside the display tank accomplished by the powerheads? How much total (sump + display tank) turnover do you recommend for an SPS reef tank? (As for the sump turnover rate, some say that too much turnover in the sump (> 5x/hour) deprives the sump of sufficient time to process the water, and, hence, they recommend 3-5x turnover in the sump to slow things down there, complemented by a higher turnover in the display tank via powerheads.)

[Regarding whether 1.5" drainlines from external overflow box were overkill, uncleof6 writes:]

The original design, used 1" bulkheads, with 1.5" pipe. Build it like that, and you will have a very wide bandwidth. Capable of more than you will flow in this tank assuming a max 750 gph, which will probably be your water volume, after everything is tossed in the tank, and sump should only run around half full... 12.5 gallons. And possibly a "not quite linked yet" issue with low flow rates and large pipe, may be avoided, using 1" bulkheads. The original design works as intended.

This sounds good. Would there be a problem actually using 1.5" bulkheads, instead of the 1.0" bulkheads? I suspect that will speed up the evacuation of water a tiny bit in the external overflow box. (I've already purchased the 1.5" bulkheads.) As for the sump, it is a Trigger System Ruby 36s sump, which the manufacturer claims has an operating volume of ~25 gallons (i.e., at about half full), not 12.5 gallons. That being said, your point about better matching the internal and external overflow boxes, to avoid a "not quite linked yet" problem is probably more urgent, given the larger voume demands by the sump?

[Regarding how large the holes at the back wall should be, to drain water from the internal overflow box to the external overflow box; whether they should be larger than 1 inch in size, uncleof6 writes:]

I would make them as large as practical, for maximum "communication" between the internal and external boxes, and the less noise--1" is really too small, IMHO. The waterline should be around the center line of the holes, so you can see how limiting 1" holes are going to be.

This is a very good point. I was particularly troubled by the smallness of the holes in the design. "As large as practical" would mean what? 1.5"? What would you recommend on this Aqueon 75-gallon tank, which is 48" wide?

[Regarding how many holes should be drilled in the back wall of the aquarium, through which the water will flow from the internal overflow box to the external overflow box, uncleof6 writes:]

Number is an obscure question, and we are not dealing with a gravity/head pressure thing, rather flow through a culvert....I believe that more within reason, is better.

Also a great observation. So the horizontal flow through a culvert at half-circle/centerline is different (lower?) than the vertical flow through a pipe. Makes sense. So more holes within reason is better. I'm sensing maybe to go with a total of four or five holes, whose size is 1.5" each (not the 1.0" inch holes), equally spaced along the back would work well. Would that permit sufficient "communication" of the water from the internal to the external overflow boxes?

Thank you for your help, Uncleof6, it's most appreciated!

 

[picker]

> My big concern: only 3 holes on the back aquarium wall

SkyReef, I like it! and feel your intank 1" C2C will be perfect, perhaps alittle hard to clean. If our goal is to avoid air to eliminate noise, we need to watch water velocity that could possibly splash or cavatate. So more or larger holes will slow down the flow and decrease chance of air. And if you can keep the holes underwater (i.e.: as low as possible) that will also decrease the chance of infusing air from water velocity.

so use more possibly smaller holes as low in the C2C as possible.

This is about 1000gph across 30" well attached to the C2C and no splashing on the far side.

 

[SkyReef]

> My big concern: only 3 holes on the back aquarium wall

SkyReef, I like it! and feel your intank 1" C2C will be perfect, perhaps alittle hard to clean. If our goal is to avoid air to eliminate noise, we need to watch water velocity that could possibly splash or cavatate. So more or larger holes will slow down the flow and decrease chance of air. And if you can keep the holes underwater (i.e.: as low as possible) that will also decrease the chance of infusing air from water velocity.

so use more possibly smaller holes as low in the C2C as possible.

This is about 1000gph across 30" well attached to the C2C and no splashing on the far side.

Hi, Picker:

Thank you for your quick and informative response. Thank you also for your picture. It is helpful to see what you are talking about. I have a few follow-up questions, if you don't mind.

Regarding holes that are drilled in the back wall of the aquarium, to accommodate water transfer to the external-overflow box: It makes sense that such holes should be larger than 1.0", or there should be more than 3 holes that remain sized at 1.0". This makes sense because the larger capacity for water-flow would cause the velocity of the water passing through each hole to be lower, than if using only three, 1.0-inch holes. This being true because the total volume of water passing through the system would have more space to pass through at each portal, lowering the water pressure at each hole. Perfect. Thank you.

As to your point about making the holes as low as possible in the internal-overflow box: This point makes sense from a water-pressure perspective; the more weight of water above the holes, the more pressure placed on the evacuation of water through the hole, for a higher flow rate. Notwithstanding this higher flow rate (which could cause air/water noise), the risk of water/air noise is offset by the fact that there is a greater volume of water above the holes--i.e., the air column is farther away from the hole, separated by a greather thickness or depth of water--lessening the likelihood that air will get introduced into the water that exits the internal-overflow box to the external-overflow box.

But here is the question or discrepancy between other answers given on this point: you say the holes, ideally, would be completely submerged, but others suggest that the water will reach a height of only mid-circle/centerline of the holes, not a height above the holes, altogether. I wonder which would be the case. Have you seen what the result is in this internal/external-overflow box using a BeanAnimal setup? Which result actually occurs, mid-circle/centerline-of-hole submersion or a compete submersion of the holes? If the answer is that the height of the water depends on various factors, what are those factors? How can I ensure that the water will completely submerge the holes, other than by placing the holes on the back, aquarium wall at height just above the bottom plate of the internal-oveflow box? Advice here would be most helpful.

As for the picture you supplied: your picture depicts an internal-overflow box, only, with no external overflow box, correct? I can't see an external-overflow box shown, if there is one. Do you have pictures of an internal/external-oveflow box, using a BeanAnimal setup?

Re the 1" depth of the internal-overflow box (front to back): Finally, it would be most helpful to learn why you think the 1"-deep (front to back) internal-overflow box (1" from back to front) would be acceptable, rather than the larger depth of the internal-overflow box (front to back) that others are calling for? I get that it would be harder to clean; that makes perfect sense. I've already purchased the glass from which to fabricate the internal-overflow box. If it is acceptable to use that 1" set-back (front to back) for the internal-overflow box, then I can start fabricating. However, based on others' concerns, I am hesitant to start fabricating right away. Based on concerns that a 1" depth (front to back) is not sufficient for an internal-overflow box, I may need to purchase glass that will accommodate a larger set back, say a 2" depth (front to back) for the internal-overflow box.

Big Picture of Functionality and Aesthetics: Although my initial goal was to have the internal-overflow box be as skinny (front to back) as possible, for aesthetic reasons, I'm willing to go with a little larger setback (front to back), if it is justified for better flow and "communication" to the external-overflow box. In this regard, I currently have an internal-overflow box, without an external-overflow box, on a BeanAnimal-design tank (a 28-gal NanoCube). While I love the silent and safe aspect of the 28-gal NanoCube, the 4-inch-deep (front to back), internal-overflow box is a little inconvenient for aquascaping purposes because the live-rock and aquascaping, piled high in the rear of the tank, is cramped by the bottom plate of the internal-overflow box that protudes a whopping 4 inches from the back wall of the aquarium. As well, the 4-inch-deep internal-overflow box (front to back) is somewhat of an eyesore on my 28-gal NanoCube because it can be seen as an artifice or contraption in the tank. That is why I wanted to go with a minimalistic, 1"-deep (front to back) internal-overflow box on my new 75-gallon tank, coupled with a hidden, 4"-deep, external-overflow box.

Your thoughts and experience are most appreciated.

Thank you.

 

[uncleof6]

I have finished my build and waiting for Rock to start cycling, because I used a 1" pipe, bulkhead and elbow for my syphon, and my open channel and emergency are 1 1/2" pipe, bulkhead and elbows, I have limited my flow rate at about 1000gph. My DT is 200g and I would like to increase flow a little. My question is when I increase my syphon, should I jump to 1 1/2" or 1 1/4" pipe, I obviously can not change the bulkhead. How much increased capacity will 1 1/4" provide, I am not looking for 10x flow, just a little more than 5x. Budster:bum:

The flow rate is limited by the bulkhead size. What an increased pipe size will do, is reduce friction loss, in the rest of the drain--only so much is going to flow through the bulkhead at a given head height. 1.5" on 1" bulkheads has a very wide bandwidth, Bean has the figures for his setup, I don't. 1" pipe with a 24" - 36" drop should do 1200 - 1500 subject to some variation. Because I don't subscribe to the antiquated rule of thumb, I would have started with 1.5" bulkheads.

 

[uncleof6]

Thanks, Uncleof6. As always, your recommendations are very thorough, detailed, and most helpful.

If I understand you correctly, the 1-inch deep (front to back) internal overflow might cause an issue with flow rate because there is not enough of a volume of water in the skinny internal overflow to keep up with the external box, which is much deeper (front to back). Is that correct? What do you think about a deeper setback (front to back) of 2 inches. Would that be sufficient?

Correct, not an indictment that there will be a problem, but more room downstream is not a bad thing. Just an indictment that I think it is getting carried away with "space saving." I see the case against 5 - 6," though even that is less intrusive, than a corner overflow, but I think 2 - 3" reasonable. What would cause a problem is a function of weir length, flow rate, and at what point the water would pile up, due to limited space downstream, as in a bubble trap for instance, rather than "drop."

Higher sounds better, I agree. Are you saying that you recommend ~ 10x turnover through the sump, PLUS additional, turnover inside the display tank accomplished by the powerheads? How much total (sump + display tank) turnover do you recommend for an SPS reef tank? (As for the sump turnover rate, some say that too much turnover in the sump (> 5x/hour) deprives the sump of sufficient time to process the water, and, hence, they recommend 3-5x turnover in the sump to slow things down there, complemented by a higher turnover in the display tank via powerheads.)

Couple of things. It is plus circulation provided by power heads. We are not going to get away from that, efficiently.

The rules of thumb, run anywhere from 20 to 100x and beyond "total." So, I think it is rather random at best. What we want to accomplish is transport food and oxygen to the critters, and waste/by products away from the critters, and out of the tank. A turbulent flow sufficient to keep the water well mixed, (no dead spots) and in motion, is the goal. There is no way we can approximate the flow on the natural reef, in a small glass box, and I think it can be accomplished with more or less than the "rules of thumb." Any "rates" set up in this manner, will cause the critters to "sway with the current."

Only way to get it out of the tank, as rapidly as possible, is to send it to the sump, for processing. It is far from a perfect processing either, as no matter how slow the flow, it will not be removed in a single pass. It is a cumulative process. This argument is circular, and isn't based on anything solid. Macro will grow just fine in 2000 gph flow, though I hardly flow that through a "fuge." The macro will use what it needs, and is independent of flow rate. The skimmer performance is based on dwell time inside the skimmer, not what is flowing past it. A properly sized skimmer (then we debate on how to size a skimmer ) eliminates the concern over flow rate through the sump. After some complicated turns, this makes "recirculating skimmers" all ad hype. But what we get with "more" is increased rapidity of surface renewal which is the goal, rather than mixing the organics back down into the tank.......

This sounds good. Would there be a problem actually using 1.5" bulkheads, instead of the 1.0" bulkheads? I suspect that will speed up the evacuation of water a tiny bit in the external overflow box. (I've already purchased the 1.5" bulkheads.) As for the sump, it is a Trigger System Ruby 36s sump, which the manufacturer claims has an operating volume of ~25 gallons (i.e., at about half full), not 12.5 gallons. That being said, your point about better matching the internal and external overflow boxes, to avoid a "not quite linked yet" problem is probably more urgent, given the larger voume demands by the sump?

The problem I was discussing, is some information, scattered at this point, of large bulkheads with lower flow rates showing some start up issues with the siphon. Bean's system does not display such issues, 1" bulkheads/1.5" pipe. The difference? The bulkhead size. It is a deduction--that is the only difference. Is the bulkhead size directly indicated (linked,) a hypothesis. Could be just an adjustment issue. What I know, at lower flow rates, the system works as designed. At higher flow rates, the 1.5" bulkheads work fine.

This is a very good point. I was particularly troubled by the smallness of the holes in the design. "As large as practical" would mean what? 1.5"? What would you recommend on this Aqueon 75-gallon tank, which is 48" wide?

Also a great observation. So the horizontal flow through a culvert at half-circle/centerline is different (lower?) than the vertical flow through a pipe. Makes sense. So more holes within reason is better. I'm sensing maybe to go with a total of four or five holes, whose size is 1.5" each (not the 1.0" inch holes), equally spaced along the back would work well. Would that permit sufficient "communication" of the water from the internal to the external overflow boxes?

Thank you for your help, Uncleof6, it's most appreciated!

See the drawing above...the motive force moving water from internal to external will be the head pressure/gravity flow through the siphon and open channel. Fewer, smaller holes will cause more intense "channeling" (think teeth on an overflow.) More/larger keeps things more "calm"