Plumbing - Beananimal drain issue

Rob.In.AZ · May 9, 2026

Here's the situation.
155g DSA Pro 3x 1" drains, 2x 3/4" returns.
The drains are a straight drop to the sump. Literally, straight plumbing.

Increasingly, when I shutdown the return, typically for a water change or whatever, when I restart, the 2nd drain drains, and the main drain does not. I can adjust the valve on the main, but it will not drain. In the past I was able to completely close the main, let it sit for a few seconds, then completely open it and get it going. Now that doesn't seem to work, and I have to pull out the stand pipe. That usually gets it going.

I assumed initially it was a blockage, snail found it's way down there or something. But, not the case. Buildup of some kind was my next thought. I have a piece of dowel that I can literally feed through the drain all the way to the bottom of the sump. Also pulled the stand pipe and cleaned it. Also replaced it.

Everytime, no matter what I need to pull the stand pipe to get the drain going.

Anybody know what's going on? What am I missing?

It's a PITA to pull the stand pipe and then put it back with the tank running. The overflow box is not easy to reach/ see into.

Fish Fan · May 9, 2026

Maybe @BeanAnimal will have a few minutes to try and help

Mebbid · May 9, 2026

If the main drain doesn't start when you restart the flow, then it's an airlock. The weight of the water cant push the air out of the pipe. I solved this on my tank by drilling a small hole at the top of the U to let air out. It works like a dream now.

areefer01 · May 9, 2026

Use your favorite search engine and look for Bean Animal Overflow on Reef Central. Huge archive with just about every question asked with answers. Split thread to boot. Should be easy to find and your answer.

Submerge · May 9, 2026

If I understand you correctly just leave the standpipe on the drain with the valve out. You don’t need it. Adjust the valve until it just barely puts a trickle down the other pipe. I’m running one this way now. Is the other end of the pipe in the sump submerged? Should be for best operation to get the syphon

BeanAnimal · May 9, 2026

How far under water do the standpipes terminate? The "main" that will not start is likely due to it being air locked. Drill a small how or two in it at the sumps normal operating level to allow it to purge air when the return pump starts back up.

Rob.In.AZ · May 9, 2026

BeanAnimal said:
How far under water do the standpipes terminate? The "main" that will not start is likely due to it being air locked. Drill a small how or two in it at the sumps normal operating level to allow it to purge air when the return pump starts back up.

Makes sense. Must’ve had just enough pressure build up to break the air lock on occasion.

I was working on the assumption the siphon was the “quiet” part of the quiet, false overflow. But it makes sense that that would fix it up

Thanks to all for the help! I will drill it out and see if it fixes it