This might help to get the plumbing from the compressor into the PVC securely and get the air going the right direction too.

Long Bend Wye/Tee
http://www.homedepot.com/p/NIBCO-1-1-2-i...HD112/100345167
(Also the long bend might make a nifty handle for underwater use.)

Adapter to step it down to 1/2" threads. Inserted into a T of some sort.
http://www.homedepot.com/p/Charlotte-Pip...050HD/203811535

I was thinking about the double 90's that we commonly use on our larger airlifts and how far into the pipe that would stick and restrict the pipe, not to mention it would be almost impossible to make such a connection. So I would look into the long bend T and the adapter's I linked only raises the price a little like $5 or so, you can just use a standard T and a reducer bushing as well.