New sump/fuge/skimmer up and running!

Check valves can fail. Most people are against using them. Easiest thing would be to put the return lines close to the water surface so they dont siphon back to much. mine cut siphon before my overflows even done draining.

 

That's pretty much what mine does--there is very little water that comes back into the sump when the power is out.

 

That and drill shiphon breaks in your return lines. They need to be big enough to not clog eaisily. siphon breaks can clog as well, but mine were easy enough to see they were flowing. Drill them just below the water line to make sure they do not splash.