Looks like your running a Durso style drain. With the air bleed home on the 1st 90*. I have tried that way too, and didnt like it much. I found using a T, and having the air bleed on the other end of the T performs much better
If you look at the one in the pic here, you will see what I mean
http://www.dursostandpipes.com/
when a Durso air bleed gets pluged, it will surge in and out of a full siphon. Trick with them is to ballance the air bleed with the amount of water it should flow.