Hook directly to the city water and don't bother with using your fresh water tank and pump. Always leave your valves closed until ready to dump the tanks especially the black tank. Sewer flies will invade your tanks and then they will get into the trailer every time you flush if you leave them open. Also, you don't want to dump your black tank until it is at least 3/4 full or full. Full is better because the solids need the water flow to be flushed out. If your unit has a tank flush fitting then use it too when dumping the tank. Solids will build up in the tank if you don't have enough water flow to get them out.