We just bought a Sunset Trail 24BH and took our first trip last weekend. Aside from the usual "duh" moments, there's one thing we still haven't figured out. When we left the house, the freshwater tank gauge showed empty. When we got to the campsite,we hooked up to city water. When we were leaving the campsite and dumping the black and gray tanks, we noticed the freshwater tank gauge showed"full". We never used the water pump; the pressure from the city water was all we needed. SO HERE'S THE QUESTION...why did the freshwater tank fill? Is this normal? Is there some switch to close off the freshwater tank when we're using city water so we don't have to lug around 40 gallons of water when we leave or waste the water by dumping it?