As I said before, my return goes 2" below the water, I have 5 holes all about 1/8", looking closer, 2 of them are at my "ideal" cut off (just at where the overflow box would stop flowing), 2 of them are another 1/2" below that (and the sump could hold the water if it came down to it), and then the last one is an "Oh hsit" hole (i made it a bit bigger, and it flows some water out so I set it in a direction to supplement my outflow). I havent tested the sump to this hole, i'd probably have a FEW gallons on the floor, but way better than half a tank
Also, as part of weekly maintenance I just take a baby bottle bursh (the little part made for cleaning the nipples) and clean out the holes... Remember nothing is a free lunch in this hobby
(advice i should remember myself
)