Ok, out come the Forstner attachments!**
(drill bits are fine, Forstner are best... and really great for all sorts of stuff...)
take it slow, and in steps, and cut all the way through the MIDDLE of both pieces. you're using 7/8" drill bits
, as, the PVC will fit snugly in the holes you drill. Nothing fancy here, just drill straight through.
Now, pull out the ruler** and sharpie** (for you chaps in the UK, and people in the rest of the world, a sharpie is a permanent marker... sharpie brand is the best though. Correct me if I'm mistaken, but for some reason it's mainly a US brand and other countries don't seem to know of them, how sad.) and draw two tangents to the hole you just cut. opposing tangents are best... (see below) this is where we'll be drilling for your air lines. (only one for the Archimedes screw type)
** available at Amazon.com!