Can't get drains to work consistently


New member
I've been messing with the drains on my tank for the past year, trying to get them to 1) behave consistently and 2) limit the bubbles in the fuge area. I'm not worried about bubbles in the main sump area because the drains go into a filter sock.

So, to my tank design. It's a 6'x4'x2' tank, approx 330g with two drains. The left drain is primarily for the fuge, but I need an overflow to the main sump area so I can control how fast the water is going through the fuge.

The right side drains primarily into the sump, but I also T that off to my chiller, so I need to be able to control the flow to the sump portion so I can adjust the flow amount through my chiller.

My return pump is a Dart pump with a 1 1/2" outlet.

I've tried various sizes of pipe, from 1" to 1 1/2" for each drain, reverse Durso's, etc. Still, I must be missing something. Here's a picture of my latest attempt for the fuge drain.


The pipe is 1 1/4", and the union near the top is the connection to the drain. On the left is the drain into the fuge. The pipe goes down into the fuge, to a 90, when then connects to a T. On the left side of the T is another 90 which is the water outlet into the fuge. The top of the T is connected to the pipe you see at the far left, which is a breather pipe to let out any air.

The T to the right is the overflow to the main sump. I have tried using pipe both with (as you see in the pic) a breather tube and without (using a 90, instead of the T to take the water down into the sock).

Unfortunately, I get an inconsistent amount of water draining into the fuge area. Sometimes, I have good water flow, then all of a sudden, it will change and there will be less flow. There is also an extreme amount of air getting mixed in (producing lots of bubbles). This also changes how much water can drain through the pipe, which changes the water level in my overflow.

I also have Durso stand pipes at the top of the drain that are made with 1 1/4" pipe.

So, before I start yet another re-design of the drains, I thought I'd post here to find out what I'm missing, doing wrong, etc.




New member
Well it sounds like your plumbing is creating an almost 'complete siphon' then the siphon breaks.

It's possible that you are just having a fluctuation with the Durso.

Have you played with the hole size in the Durso's cap? Usually when a fluctuation like this occurs, usually people start by drilling the hole out larger.


New member
I had it running with smaller piping (1" on the drains) for about a year, but could not run the return pump at 100%. It ran this way without any real issues. It was a pain to balance at first, but once I did (including mucking with the hole size on the durso) it worked fairly well.

However, now that I want to turn up the pump and increase the flow to my fuge, I started having issues with the drains (two 1" drains) keeping up with the return pump. So, I need to increase the pipe size.

I don't think that just increasing the pipe size on the drain (the durso's have always been at 1 1/4") would cause a new problem with durso's, but I'll keep that in mind.

Keeping in mind that I'm not real concerned about bubbles (would like to reduce them in the fuge as much as possible, but not real concerned here), what would be the best drain design for maximum (non fluctuating) water flow?

Reverse Durso's, straight pipes, something else?

EDIT: Would like it to be as quiet as possible also.



New member
You have a rather large aquarium. I do not know which Dart Pump you have or its gph rate ... but I have a feeling that you might be right about your plumbing size. It could be a tad too small.

I just set up a 75 gal tank that uses two 2" Durso standpipes (1 overflow in each corner). This is very quiet so far ... no problems. shown here and shown here I just like to oversize stuff in case of future changes.

I may be the elaborate plumbing, restricting valves, and horizontal running pipes that is trapping the air.


Premium Member
You would have better luck with both in the same box.

1 Set to full siphon via a ball valve and the other setup with an air hole (durso style) and wide open. It will pick up the slack tha that the siphon does not handle.

This will be dead silent and introduce very little air into the sump (as long as the open durso does not have a high flow it will not draw a lot of air).

The setup is very self tuning, but ideally would have an emergency standpipe in case things did get out of whack. At system startup the full siphon can take a few moments to purge the trapped air get going at full tilt.


Premium Member
Not handy...

Ideal Setup:

1 Overflow box
3 standpipes

Standpipes setup as follows:

Standpipe 1 has a down turned elbow. There is no "air inlet" as you would find on a stockman or durso. The standpipe will have a ball valve on it.

Standpipe 2 has a down turned elbow. There is an air inlet on the top of the standpipe. Ideally this air inlet will have a john guest fitting on it that is attached to an air line. The air line will be curled over and clamped just below the top edge of the aquarium trim. (More on that later).

Standpipe 3 has an upturned elbow with a strainer. It will be set so that water will flow into if the water level rises above the normal operating level of the overflow box.

How it works:

Standpipe 1 is throttled back with the ball valve until the water level in the overflow box rises enough to keep the standpipe from drawing in air through its down turned elbow. This means it is running at full siphon with NO AIR! Very efficient!

Standpipe 2 is wide open AND has an air inlet. This will handle the flow that that standpipe 1 is rejecting (by your ballvalve setting). The air line is positioned in the display so that it will become blocked by water if the level rises too high. This will block the air intake and turn standpipe 2 into a full siphon (much more capacity than open channel flow). This will prevent the flood.

At the same time the intake on standpipe 3 will be handling the excess flow.

It is a very failsafe system and dead silent.


New member
I think this is what Bean means ... well something like this:


This is one of my overflows. It’s not completed yet, but you can see how it works. Basically this overflow is completely running off of one 3/4" bulkhead. I used a 3/4" gate valve to throttle back the flow in order to adjust it. If I had this valve wide open then it would complete drain this overflow down to the bulkhead. I will soon slap 2 elbows on a little standpipe for this bulkhead.

The other large 2" elbow is for my Durso standpipe. As you can see in the picture, I have my Durso valve shut off ... since it's not installed yet and no hose runs to the sump.

If I had both the Durso and the gate valve open then practically nothing could cause a severe fluctuation.

BeanAnimal evidently uses 3 standpipes ... I just use 2.


New member
I think I've got it, but that would take some major retro-fitting. I'm not to sure about that right now.

Any other suggestions for my current setup?