Hello,
I need some advice on which size pipe, where to put the overflow, how many i need on my new project tank.
It is a bowfront 86x29x29 (24 at end). It will be a freshwater tank.
Thanks
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My calculations come to around 300 gallons.
1.5 should be plenty. Many people have end overflows, mostly on a peninsula style tank.
A Bean Animal drain will be the quietest (3 pipes).
Plenty of information here if you do a search.
It really depends on what your flow through rate is going to be. I have just under 3000 gallons per hour flooring through my overflow. I have 1.5" drains and I wish I went 2"
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I would still use 1.5 in case the focus changes later on.
You can get the flow you want with that setup, but if you can increase the size of the drain pipe to 2", you'll be better off in the long run since biofouling will slow it down a bit over time. I have a 30' horizontal run with 5' of drop. Using 2" drain pipe with 6 sweep els. I have plenty of flow to support 1500 gph +. I run 1300 gph (measured with the apex flow meter) and have the drain valve closed more than 1/4 of the way.
When I first set up my tank I ran 1.5" drain pipe and within a year it was having a hard time keeping up with the return pump. My guess is that it was draining around 1200 gph max.
Your 12' of drop will help substantially and you probably will get away with 1.5" pipe, but I'd go with the 2" for the extra headroom.
I'm not sure I understand how the pipe would run if it is above the steel, but I wouldn't be too concerned about a horizontal run with your 12' of total drop even if it has a small rise in the middle. Keep in mind that the flow will be dictated by your return so I would keep that at around 1500 gph there shouldn't be much of any buildup of detritus in the drop area. I would use 2" pipe for the drain to give yourself a good sized margin of error.
You can eliminate the small risk of an overflow in the tank from the unlikely event that the drains get clogged by designing your sump so that the total volume of the return section is less than the unused volume of the tank when normally operating. In my case, the return area is about 10gals and I calculated that I have almost 15 gallons of space between the normally operating water level and the very top of the tank.
The other side of the equation is to make sure your sump can handle all of the water draining from the tank in the event the return pump stops. With 40' of 2" pipe and whatever the return lines will siphon back, that's a good amount of water you have to account for.

1-What is the purpose of the Tee with the cap at the back of the internal box design?
2- Also, I was wondering if instead of the airline on the open channel, would a hole drilled in the top of the 90 inside the tank work the same?
Ok so my Question is about gatevalve placement. I'm running a calflo overflow on a 2 ft high tank. The stand is 3 ft high. I would like to put my gatevalve about the bottom of the tank which is about halfway to the sump. I've read about it being ok at the top and bottom but cant find anything about how it works in the middle. The reason I'd like it there is I plan on switching to clear vynil tubing after the gatevalve and if I place it at bottom of tank/top of stand i can secure it very well to the stand. Any input is greatly appreciated.
In the BA overflow box esternal the syphon and the other drain are not at the same level.
Does in a C2C internal overflow, it is better to drill hole in the back at différent height ? The full syphon 1'' lower than the 2 others pipe ?
Thanks
If it were me, I would do it without worry. It's not going to impact the flow and I doubt it would increase the chance of a clogging over time. You could put a clean out at the drop if you wanted for extra peace of mind.