How big of pvc pipe do you need to house a goldentail or a fimbriated eel? I have heard that 2" is a good size. Or will the girth of them get bigger than 2"? I am considering keeping 2 eels that get around 2' to 3' long.
It'll vary...Goldentails are much slimmer than Fibriated. You'll get some morays that'll have a 6" girth, or more.
Also...you keep a Fimbriated in the tank, with anything else and you'll soon have a "Fimbriated species tank".