I found out through class that it is now against code to use air to test plastic supply lines. This is because the oil eats away at the rubber "O" rings in adaptors which seems stupid to me because I never use CPVC adaptors which have the "O" rings in them, I always use the CPVC/Brass MIP and FIP adaptors anyway. I have tried the CPVC adaptors with "O" rings and have broken them. way to brittle for me. We can still use air on PVC waste, and copper supply though.