is there a trick to matching return flow on a herbie?

[Dez]

If you are planning on running your wavebox, then I would tune it with the wavebox. That's what I did and no problems. If you tune it without the wavebox on, then once you turn the wavebox on the surging water could potentially surge in and out of the emergency standpipe (which is what happens if I run my overflow box water level too high, then it gets loud). Hope this helps.