There are different grades of plastic, and many fuel tanks are made of it, including the large square 5gallon pure alcohol cans for race track use.
PVC is not the same plastic, but has worked for a lot of people to make go cart, mb, and generator tanks.
Maybe the shutoff I got from Sick was American threading then. It was a BEAR to get in the china kit tank. lol.
Here, I used this on a home-made intake manifold and it worked. It says solvent resistant on the package and 3200PSI strength on aluminum to aluminum. http://sadpanda.us/images/601540-VL73CZR.png