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
2 Labradors, both yellow Males - Bailey and Angus. Both rescues, both 10 yrs old.
02 Georgetown 325, F53 V10