I've installed a new pump and filter for an in-ground pool. Ive also installed a check valve from the pump to the filter inlet. The problem I have is when the pump turns off, I see some diatomatous earth back flow into the pool (not a lot but enough to irritate me). I've also noticed that the pump bucket (I'm sure it's not called that, but it the thing with a clear cover) has very little water in it after being turn off for awhile (hours). It doesn't makes sense since the inlet to the pump bucket is higher than the outflow which is at the bottom of the bucket...any ideas? Maybe another check valve between the pool and the pump?

Pool & Spa - Water Pik - Flow Valve Assy. Series II Bronze 325