Drain noise on a DIY SM100-style scrubber

I've got a DIY scrubber that is similar to an SM100, except that I stretched it to 10" tall to fit 6 T5HO bulbs instead of 4. It is working fine except that my drains are sucking air and are gurgling noisily. I've got two 3/4" bulkheads for drains. They suck air when full open with a 1" hole and when restricted to a 3/4" hole. There is around 1-1.5" of water in the chamber when running. I can tune the water level by opening or closing the flow (both the inflow and the drain flow), but I've been unable to stop the gurgling unless I just about fill the chamber with water. Are there any tricks to keeping the drains from sucking air? Would anything change if I go to a single, larger bulkhead?

Try routing the drain pipe so that it only goes "down", and not up and down.

Also, it will quiet down as growth get thick by the drain.

Well, problem solved...
I was having the noise problem while I was water testing my new system with fresh water. I tried all sorts of things to quiet it down, but had pretty much given up.

To my surprise, when I put the salt in, the gurgling completely stopped. It seems that some characteristic of salt water makes it much less likely to form vortices and suck air into the drains. Even with my Mag 12 running wide open, what should be around 1000 gph, all I hear is a pleasant "ssshhhhhhh" of some foaming where the screen hits the water line.