Does anyone know officially (for example as per the plumbing code) how tight a threaded PVC fitting should be? I'm guessing it's hand tighten + X number of turns.
That's correct.Teflon tape isn't a good idea on PVC threaded fittings, according to the fitting manufacturers. The primary purpose of teflon tape is to lubricate the treads so the fitting can tighten further with less effort, and that leads to breaking the PVC female fittings. Instead, the use of thread joint compound, a paste, which is made for use on PVC pipe, is recommended.
Very interesting link.Also, the fittings use National Pipe Thread standard. This thread type tapers, so that the joint gets tighter the more revolutions. It should not require more than a 1/4 to 1/2 turn past the hand tight point to seal a pipe for aquarium use.
EDIT -- I found this on LASCOs site. They say no more than 2 turns past finger tight.