Drain above or below waterline?

I am really battling durso noise. I have tried one hole, two holes and fine tuning with air tubing. Multiple times I have silenced it for a few days only to have it eventually start doing the surge and drop in the overflow. It remains silent but not really comfortable with surging. If I pull the tube it goes right back to running well but air sucking noises. I feel like I have exhausted the fine tuning at the upper end so ready to start attacking the output drain, which is a straight shot down, 2 inches submerged. Would I be better to pull it out of the water and figure out a way to deaden the splashing? durso is wider than 1 inch bulkhead, drain below bulkhead is wider as well.

 

How big of a return pump are you running? I believe 1 inch bulkheads are max rated at 700 gph. And may be your issue (or not)

I just set one up myself, I drilled 3 holes with my thinnest drill bit, but the overflow level was too high, so I covered the holes with a piece of tape. stable and dead silent. I have a 600 Gph return.

The surge may also be caused by the larger diameter durso forcing the smaller bulkhead to choke down more water than it is capable of.

Take everything I say with a grain of salt though unless confirmed by somebody else, who probably knows more.

 

I had that issue where I got it fine tuned and then a couple days later noise and surge etc.

I solved it by slowing down how much water was draining. I use a ball valve on the return and fine tune that valve to where the surging stops, and with it the noise.

 

My pump has a dial to lower the flow so I will give that a try...thanks! I am running an undersized pump so I did not really expect that to be a problem but I will give it a try.