I have 3 water valves in my 1976 international. One is by the pressure regulator one is under the sink in the bathroom. The bathroom is a center bath. Also there is one under the kitchen sink. Im not sure what they do. Im positive the one at the rear by the pressure regulator is a drain valve. The one by the kitchen sink is either a drain or you can open it to fill fresh tank im not sure. And im not sure what the one in the bathroom does. Maybe a water heater bypass when winterizing? Any info would be greatly appreciated.