OK, so I also had the usual durso problems of gurgling, levels going up and down in the overflow etc. Here's how I solved it, without continuously drilling/sealing holes etc.

Create the standpipe in the usual way, and use a 1" cap at the top which requires you to use a piece of normal 1" tubing from the T piece to mate with it. Glue the lower half of the 1" tube in the usual place, so that there is enough of the tube sticking out of the top of the T piece to allow the cap to rotate.

Drill various holes around this piece of 1" normal tubing of increasing size.

Drill a hole equivalent to the largest one you drilled in the 1" tube, at the same height as the holes in the inner 1" tube, in the cap.
The idea is that you can rotate the end cap around, to let in differing amounts of air until you find the hole on the inner 1" tube which is right for your setup.

I hope this makes sense, after building one Durso and enlarging the hole until it was too big, I thought this setup made a lot more sense. In my experience the problem I found is that I consistently made the hole larger than it needed to be.

Let me know if you have any questions.

- Tim