Look around all sides of the fresh water tank. If the pipe you saw from underneath is a tank drain, there will be a valve very close to the tank. Also, your water pump will be in that area. That will be the place to start trouble shooting. If you have a winterization line, connected between the tank and pump, make sure that the valve is in the correct position (try both directions with the pump running and sufficient water in-the tank). If it pumps water from the tank, good, if not start with pump clean strainer, obstruction diaphragm etc. Then down the output line to fixtures.
Ken
