that is easy my friend
just drill a hole in the return pipe just above the water line and that will act as a siphon. I would put it in the back facing the wall of the tank thou so you dont get any spray thou IME

Use some True Union Check valves?

I've had then on all my tanks, and never failed me.. the swing gate has no metal springs to rust, so should never stick open.

i was thinking check valves but they can fail and it reduced flow on the pumps but alot.

do you mean in the sump part or in the tank part?

I'd never build a system without them... and because there isn't any metal parts there really is no place for it to fail. At least not on the ones I use. It's just one extra fail safe..

Based on how low your returns come in on your tank and siphon break is going to be tricky becuase the water is gonna drain down to those return bulkheads, which is why I gave the suggestion of check valves. Unless I missed something on your plumbing system.

ok... You posted this earlier... but later on you mentioned your CL was running thru the manifold instead?...

So does that mean your sump return is coming back thru the 4 bulkheads in the tank?

http://i300.photobucket.com/albums/n...Manifold-1.jpg

no that diagram is kinda messed up , it would return just through the top 2 holes

hey man i see that you went with the 45 in stead of the 90 you will see alot better flow and less head loss on 45 then 90 and it looking pretty fancy now

He was talking about the Tank water line. Which means for a siphon to work, your return plumbing needs to higher than the water line... You will usually see a siphon break on plumbing that comes up over the tank rim and back down under the water.

That's why I suggested check valves, because I was (and still am) under the impression that your return plumbing comes back in on the top 2 bulkheads on the back of your tank?

yeah that is correct, the returns are just the top 2 on the back wall of the tank. originally i was going to use those for the CL but changed my mind after i got the tank.

yeah i did, it does look better with the 45.