First I would like to say I do not have a drain like this and I am not an expert. But what I read on this sight I thought the pipe went straight threw the dam not up and over. The way your picture is you only have a small % of suction, the exit pipe is only a little lower than the inlet pipe. Suction should start when water covers the air pipe B. Again I may be wrong.

61 acre water shed lake. bass, channel cat, black crappie, wiper, walleye, redear sunfish, blue catfish and bluegill. To many bullhead and common carp
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