Surge device, closed loop or bigger powerheads????????

[Delphinus]

Did you use the check valve on the discharge tube? I haven't finished reading the thread yet but the gyst I'm getting is that this is integral to the flapper closing properly. A P trap may work as well except an open P trap would defeat the purpose of capping the overflow.

Although I think the problem would be different from what you're describing.

Ah, time to read it again and think it through one more time.