Restarting overflow- not priming


Premium Member
I have a 1600 gph cpr external overflow. My problem is every time I turn the pumps off to feed and then turn them back on, the tank will overflow if I don't wiggle the drain pipe. The overflow just starts filling up with water and doesn't drain. I had a piece of pvc pipe with holes drilled in it placed in the drain hole to help with the gurgling noise. I thought that was the problem so I took it out and it still does the same thing. Any ideas? I'm sure there is a simple solution that I'm just overlooking. I really don't want to come home if the power goes out for five minutes and then comes back on- causing my tank to overflow. Thanks.
Using an Aqua lifter pump on your overflow or Venturi should fix that up :) I have an Aqua lifter on mine, always restarts perfectly. Hope that helps
Maybe I should have worded that differently. It primes, but when the water goes into the back of the overflow, it doesn't start flowing down the drain hose and the overflow begins to fill up. So the water doesn't drain down and the aquarium begins to fill. If I grab the drain hose and shake it a few times, then the water begins to flow down the hose. It's not stopped up. I've already checked that. Thanks.
Sounds like you get an air bubble trapped between 2 opposing forces. When you shake it, it allos some ater to slip past the bubble, which then forces it up. Does your outlet into your sump terminate below the waterline? If so, then you get the same effect that you can have with a drinking straw, and you'll need some way to bleed the air out.
The outlet into the sump terminates below the waterine. However, I have a separate refugium that I have plumbed into the sump. My drain tube has a T in it and one pipe goes to my refugium and the other goes to my sump. The refugium pipe terminates above the water line. The sump pipe terminates below the water line.
your drain hose is the problem

you either have what is called a pocket in it or it doesn't slope enough

make sure that from the overflow box to the sump the drain line is always flowing downward with no down then up pockets and minimal horizontal runs. this may mean shortening the drain hose.

another pontential - is you may have some algea or other build up in the drain hose slowing down the flow.

the issue the way I'm understanding it is you're getting an air pocket untill you shake it loose then the hose fills with water and creates enough suction to continuosly pull water from the overflow box. that is until the pump is turn off again.
A thought might be to drill a hole in the pipe where you suspect the bubble to be and insert a length of air hose with the other end attached to a venturi valve on a powerhead somewhere. When the power comes back on the powerhead will suck any air from that tube in your overflow drain.
I found the problem. It was just the positioning of drain pipe and the pipe that went into my refugium so it terminated below water level. Thanks guys. I really appreciate all the help.