Noisy Gurgling Overflow - SOLVED!!!!

[Ron99]

I am still fiddling with this 75 gallon tank. it has a single overflow in the upper left corner. It's a 1.5 inch bulkhead and I've got an external Durso type of arrangement. The T section is made of 1.5" PVC. I have a short length of 1.25" hose and then it is reduced to 1" hose. I cannot get this to be quiet. It gurgles loudly all the time. I have tried using everything between 1.25" hose to 0.75" hose down to the sump. The 0.75" hose made it fairly quiet if I pretty much maxed out the flow so almost no air was going down the line but then I worry about something further reducing the flow down the line and ending up with the tank overflowing. I have also tried numerous hole configurations and sizes in the cap at the top and also putting airline down to various depths. Nothing works.

I hope somebody has insights into setting up an overflow with only one drain of this type.

Here's a pic: