Why is my overflow breaking siphon??

[repair]

I have quite a few of these.... long end of the U tube goes outside the tank.

I have seen the box that hangs on the back of the tank not have a pipe in the bulkhead that attachs to the wet/dry return line.

You have to have water stay in the hang on box. what happens if turn off the pump and you pour water into the hang on box? Will it drain itself dry?

It needs to have 2 or 3" of water stay in it.

 

[fish head )'>]

seems like the the tubesare still pulling waterfrom the box even when the pump shuts down. It is draining the overflow box inside the tank till it is much lower than the tank water itself. Isn't there a way to hook up an aqualifter pump or powerhead somehow to stop this from happening? What if I got equal length tubes? would that help?

yes you can I use them on weir style overflows. It sounds like when the pump gets shut off the water going down to the sump is still siphoning water down until the overflow box breaks the siphon. that needs to be corrected. this can be done in a few ways. BUT....
I like the picture idea. Then we can see if there is something wrong with the set up or point out an easy solution.

 

[jsodwi]

I just thought of something, the bulkheads have about a 3" pvc piece coming out of it with the prefilter pad on it. This piece of pvc fits very loosely and is not glued in. If water was seeping through that would that do anything?
I have the long end of the tubes sitting in the center section outside the tank.

 

[CHOMPERS]

that's it.

 

[repair]

I just thought of something, the bulkheads have about a 3" pvc piece coming out of it with the prefilter pad on it. This piece of pvc fits very loosely and is not glued in. If water was seeping through that would that do anything?
I have the long end of the tubes sitting in the center section outside the tank.

Seen this many times... glue it and it should solve the problem.

 

[fish head )'>]

It is amazing, the brilliant minds that are here at MFK!

 

[jungledriver]

Are they the stick-on overflows? If so try lowering them a little bit. Sometimes simply placing them to high on the back of the tank will break your siphon. If setup properly the the "U-tube" that carries water out of the tank should stay full of water (with no flow) ever when the power is shut off.