Hook up your fresh water hose and fill the holding tank three-quarters of the way full. For each 15 gallons of tank capacity, mix ¼ cup bleach into 1 gallon of water. Add this solution to the water in the holding tank. Never pour pure bleach directly into a fresh water tank.
Open one faucet at a time, letting the chlorinated water run through it for a couple of minutes. You should be able to smell the chlorine. Ensure you are using the water pump and not a shoreline.
Top off the fresh water holding tank and let it stand overnight.
Completely drain the system through the faucets. Open the fresh water drain valve to help empty the tank. Close all the valves, faucets and rain plugs. Refill the water tank with fresh water.
Flush each faucet for several minutes, repeating until the tank is empty. Only use the water pump. Refill the water and it will be safe to use.