Hmm. I'm thinking this is the overflow:
http://glass-holes.com/700-gph-Overf...t-gh700kit.htm
Based on the overflow calculator, this one should be guaranteed for around 400 gph (despite the fact that it claims 700 gph).
400 gph should be, as far as I'm concerned, the appropriate flow rate for a 40 gallon. I don't want water screaming through the sump. I'm presently running two reactors (ROWAphos and Carbon), and I'll be adding a skimmer (when the system moves into the 40). I think the water should actually have the opportunity to be filtered before it goes back into the display.
If I go with that overflow, I'm thinking that two 1/2" locline returns (each with a "Y" splitter, for a total of four return nozzles) would be appropriate. These would both be fed off of the same pump. The one I have
might work, uses a 3/4 in line, and would not be able to pump enough to exceed the overflow's capacity.
I'm looking at that overflow, as Hubby is not overly skilled with plastics. He's more of a wood and wiring guy. Ideally, I would like a 9", but the glass-holes overflow boxes are only available in 6" (the link I posted) and 12".
I'm also thinking that instead of using PVC pipes, I'd like to use flexible tubing (after reading through your build thread, Greg, and seeing what happened to your little Chaeto tank). In the event we use tubing, and not pipe, if something is shifted a little it shouldn't result in any glass breakage. The sump is not a big one (Aqueon Proflex Model 3) and I could see myself messing with it's positing when I add/remove things from it.