Re: Gray water tank
Since no one has as yet responded, I'll try to help. There is a good chance that the plumbing into the tank is glued in place. I doubt that removal of the tub drain would gain anything at all. The drain lines from the sink, the kitchen and the tub probably all connect into a common drain line that then goes to the tank. There could also be a vent line, though most gray tanks don't have that. If there is only one plumbing vent on the roof, it will be for the black tank. You need to find some way to see the point where the drain line enters the tank.