stopping the gurgling
 

Know there's other posts on quieting the gurgling but seem this link on RC. Wondering if anyone here has tried similar with any luck?

i have a very similar set up vertical pipe with a tee and the elbow pointing down top is open and used a five foot piece of 5/8" tubing and man did that ever take out alot of noise almost no noise.

interesting, I dont have anything like that and my overflows are silent.

My Durso overflows nearly silent as well, it's the gurgling from the drains where they enter the sump.

my drain line drains the overflow box faster than the water overflows into the box and the air line slows it down so that the water level can rise to a set height. i have tried raising and lowering the tube in the overflow box with no success but this worked.

I have ball valves on my drains so I can against the flow so it matches the same rate at which it is returned