[tbittner]

Shouldn't there be a sealed skimmer box isolating the drains from the water in the rest of the aquarium? The water flows over the top edge of the overflow box and then down the drain to the sump.

Or you could make a durso pipe that comes out of the drain up to the top of the water level you want to maintain. In either case, the surface water is the water being sent to the sump, which is most likely where you're skimmer is.

The wall and installation looks great so far though. Well Done!