You have to find the pump. That's because, at the pump inlet there is a set of valves. You turn off the valve that pulls from the fresh water tank, and open the valve that pulls from a short (maybe 2 ft) hose curled up by the pump. Then you stick that hose inside a bottle of pink, RV antifreeze, and turn on the pump. Now, starting with the nearest faucet, run water until it turns pink. BTW, and this is IMPORTANT, don't do this until you have also bypassed the how water heater. A similar method of using two valves, to make cold water go around, not through, the water heater. You just drain the water heater. YOU DO NOT WANT THE PINK STUFF IN EITHER YOUR FRESH WATER TANK OR YOUR WATER HEATER.