I prefer to tow with the water tanks empty and fill them at the camp's filling station before setting up. How can I fill the 6 gallon hot water tank on my '07 Fleetwood Utah? I think I need to turn on the water pump but I can't access the switch without lifting the roof. I want to do it at the filling station so I don't waste 6 gallons from the (cold) fresh water tank. Thanks!