Leaking threaded connections were the BANE of my irrigation install. There were several connections I had to do two or three times before they were leak free.
What I found to work best (but again, not consistantly) was to wrap 5 to 7 layers of teflon tape, and then "pre-set" the teflon tape by "screwing it into my fist". Basically, I would cover the palm of my hand with something (usually the front of the shirt I was wearing) and screwed the male threads wrapped with teflon into the hole in my fist. It sort of seems to help push the teflon into the threads before you actually screw the male/female threads together.
If I was making a connection between PVC and copper, I usually got better results using the pink tape.
