Just bought the Fischer Wye check valve. I see that the valve ends are the same size as the pvc. So you use couplings to attach it? I don't have room for unions where it's going. I decided this was a must-have before starting the tank after seeing how quickly the syphon sucks water down to the sump when the pump is turned off. $50 is worth it to avoid flood-o-rama. Also my pvc joint compound came today so I'll disassemble the overflow, inspect everything and try again. The return plumbing has no leaks so I'm inclined to just leave it alone.