Well we all get thee plumbing blues at some piont. You have 2 opions here. Mod your overflow box by drilling it for 1 1/2" pvc or returning it and getting a different one. If you return your box you will just end up with the same problem. 1" pvc is 1" pvc. Your other option is to dail down your mag 7. What size tank is it? you may not need that much flow through your sump.