Is the leak on the "intake" or "output" side of the tank? The plumbing diagrams for these campers are simple, and a fair portion of the pipes are routed underneath. The only way for there to be a leak, is for water to be getting in there somehow. You would need to look at the diagram for your camper, or trace the plumbing, to see if there's a valve to prevent the "city" water from filling the rest of your system.
1995 Toyota 4Runner SR5 4WD 5 spd
2002 Eagle Summit 12