Yea, I would just put a black lid on it, or paint the top piece of glass black. That way, you can view the overflow box from the back to make sure nothing escaped your tank and is hiding in there (fish, snails, etc.)
Where does that emergency drain go? To the sump? Or, to a sink drain or something?
Yea that's what I was thinking.......The overflow box has a cover that came with it from the builder. I know my current tank has crazy algae growing in the boxes from the residual light of the tank. I guess I'll try it with just painting the top for the time being and see what happens.
The center pipe (1 1/2") on the overflow will be connected back to the sump. I doubt that pipe will ever even get wet with the other 2 overflows being 1 1/2" But that depends on how much flow i loose on the Dart pump with all the elbows in the plumbing return lines.