What water filter did you change? My coach had a water filter in the kitchen to filter the water before it came out the faucet. There is usually a small water filter on the suction side of the pump itself. This filter is just cleaned, not changed. If the gasket on this filter is not sealing properly, it will suck air when the pump is running. Since it is on a non-pressurized part of the water system, it may not leak at all while sitting there. When hooked up to the campground water does not flow through the pump or the input filter.