Def skip the check valves. The GH overflow with only go to the bottom of the teeth and like Juan said just raise the return nozzles to a point where the water that drains back won't overflow the sump.
Okay I looked last night and couldn't find them but then again I was there for an hour looking at all the other fittings Lol gotta go back anyways so I'll look again
Oh alright awesome. The earlier the better, maybe 10-11?