Bad gas need to drain the tank of a 2000 montana

There's no drain on the bottom of the tank on these, and the fuel pump and level sensor assembly is a real ****** to reinstall because of the way the o-ring is designed. It sounds like there's a good chance you've got water in the tank, though, and you want to get that out of there pronto; there are various steel lines and such which will corrode and start shedding rust flakes if you don't. If the tank is full, this is not really practical to attempt without a transmission jack, so you'll need to siphon the gas out first. Get a replacement fuel pump module o-ring FROM THE DEALER to make the reinstall easier, even if you are replacing the pump. Dropping the tank when it's nearly empty is no big deal; any of the repair manuals can step you through that. You won't get all of the water (and other crud, if there is any) out of the tank without doing this, though. When you reinstall the pump module, use some grease or vaseline to stick the o-ring into place on the tank, and then get a helper to hold the flange of the module up against the inside of the retainer collar while you get the collar started onto the threads and tighten it down. This will give you the best chance of getting the o-ring to stay in place, in my experience. If the o-ring is just a trifle small and won't slip down into the groove on the tank, stretch it a bit and it should be more cooperative. The aftermarket ones tend to be a bit too big, and there's not much you can do to get them to work.