Drain sucking

[shipwreck]

So water testing my new setup and all is good except for the noise.  I have a dart for the return pump and an external overflow. The overflow has 2x 1.5" bulkheads in the bottom and one on the side for an emergency drain. I found that if I have 1 drain elvated slightly forcing most of the flow through the other that is the quietest mode. Only problem is the. That every few minutes a vortex forms and makes a loud sucking noise.  I forgot to mention on the outside of the bulkhead I have it T'd with one side going up to open air the other s the drain. 

The dart also feeds 3 other tanks and the skimmer so the main tank isn't taking all the flow.

Any suggestions?

 

[phi delt reefer]

Pictures would help.

Try closing off the full siphon slightly and see what happens.

That or raise the second drain a bit. You gotta play with the standpipe height to force more water into drain one

 

[Duke]

The first one should be valved, the second need a hole in it to keep it from siphoning, add an air line just above the waterline.. If the level raises to submerge the hose then it will kick in full siphon also.

 

[Neopimp]

Close the valve in the lowest drain until the water in overflow starts to rise.  It will rise until it hits the second drain height. You are aiming to get a trickle  if water down the second, and a full siphon down the first.  If you are have issues with whirlpools,  A but of egg crate across the surface of water stops it. Or raise the send drain higher or lower the first one.  Just put more distanxe between them.

The last emerg drain should be about half to 1inch below your absolute maximum water level.

 

[Neopimp]

The drains are vertical through the bottom.  You don't need to have 90s or anything at the top if the pipes.  A straight pipe will work.