Well I've been playing around with my Durso standpipe all evening
trying to get super quiet flow and have made a few discoveries.
No matter how much I messed with the air hole on top of the pipe it
was always sucking a ton of air cause it could out flow the pump
so water is falling all the way down the pipe to the sump.
It was incredibly noisy and totally unacceptable. From I could find on-line
the air in the pipe is normal though.
After much tweeking and playing around I found if I close the overflow pipes
ball valve to just barely match the output of the pump, the drain pipe fills
with water and ALL the bubbles go way and the whole system is bone quiet.
All you here is pump, otherwise you would not think any water was flowing.
Here's the problem. If the ball valve is just the slightest bit off the water
level in the pipe will slowly fall and you get air again. Or its not draining
enough and the aquarium starts to overfill.
Solution I have come up with is to close the main standpipe ball valve to
where it just barely will not keep up with the return pump. This will create
the slightest trickle of extra water over filling the tank
I will drill another hole in the back of the aquarium for a secondary overflow
pipe that will just have a simple upturned 90 elbow that will allow the extra
trickle to overflow down it's own small pipe that will dump into the top of the sump.
Its flow should be so minuscule that it will not make any noise on its own.
Right now the standpipe ball valve is dialed in "just right" and matching the
pump so I may see how this holds up for now and let run a few days while
I'm around to watch.
Really is cool how quiet I got it. Just a slight hum from the Mag-5 pump.