On my 325 ('02) the water tank is in a cupboard underneath the bedroom wardrobe/drawer cabinets, with the pump alongside and a drain valve which is connected to the tank overflow line and goes out to the back bumper area.
Originally, I thought they were dummy cupboard doors, but discovered they were "permanently" closed by a woodscrew in each door to the frame. They now have magnetic catches. With the bedroom slide closed, the foot of the bed blocks off the cupboard.
Frank and Eileen
No longer RVers or FR owners