How long is your M.H.?
I have a 1997 36' Dolphin M.H. and the water pump for the coach is located under our bed adjacent to the water tank.
A little after I bought the M.H. the water drained out of my tank and clasped.
When I took it back to the factory they took the two Air vent tubes one on esch side of the tank that runs from the top of the water tank to two holes in the floor so if it should over flow the exes would drain out on to the ground which it did.
They put a loop in each tube to break the vacuum from siphoning the water out.
If your bed is located in the back of your M.H. check under the bed and if the water tank is their then the water pump should be close by.
Just a thought.