[homer1475]

Its a herbie setup, no? 2 drains and a return?

What I do to tune my herbie in, shut the gate valve all the way. When water starts crashing down the emergency line, open the gate a little bit, then just keep opening it until the water in your overflow is just trickling down the emergency. You'll probably only end up opening it not even half way. So don't get discouraged if you only have to crack the gate valve. The idea is to equal out the flow coming into the DT from the return pump.