I recently purchased 2002 Four Winds Windsport Class A motorhome. On a recent weekend trip when flushing the toilet, hot water would flow in it instead of cold water. We were connected to city water at the campground. This only happens when connected to city water, not when using the water pump. The pressure at the campground wasn't very high. We were at a campground a few weeks earlier with no water hook-up and used the toilet with no problem. I'm guessing that the hot water is coming from the water heater inlet because of the low pressure of the city water. The water lines all seem to be connected properly. I'm thinking a check valve at the inlet of the water heater might solve the problem. Does this make sense? Any info would be appreciated.