Originally Posted by cmor1701d
Make sure the outlet is UNDER water.
I agree with "under" the water. Also, what size return pump are you using for what sized tank? Maybe you have too big of a return pump creating too much water fallind down into the sump??? Thats just a guess. How do your overflows sound, are they quiet?
I'm not following your diagram. At first I though it was your overflow because of the air hole, but I can't see where the water would drain into it.