Hook the RV's waste line to a septic system and detach the fresh water hose from the input port. If on, turn off the water heater and allow the water to cool.
Pour ¼ cup bleach for every 15 gallons of the freshwater tank's capacity into a bucket, along with about a gallon of water.
Pour the bleach mixture into the input port for the freshwater holding tank, using a funnel to avoid spillage, then attach the hose to the input port and fill the remainder of the tank. If the RV has two freshwater tanks, repeat the process for the second tank. Detach the water hose and plug the input port.
Turn on each water faucet one at a time (both cold and hot water) for a minute or two, until the odor of chlorine is unmistakable, then turn the faucets off and allow the chlorinated water to sit in the system for at least three hours (overnight is best).
Open all faucets and allow the tank to drain (you will hear the water pump engage; if you don't, make sure that the fresh water hose is not hooked up outside). The process can be sped up by opening the exterior drain valve, but make sure the draining water goes into the septic system if possible (this dilution of chlorine should not be an environmental hazard, though it may stink).
Attach the freshwater hose to the input port and fill the tank(s) to capacity. Turn off the hose, then open all of the faucets in the RV and drain the tank(s) completely. Repeat this step at least once, or as necessary until the odor of bleach is undetectable in the water flowing from the faucets. Dump the wastewater or gray water tank (if the RV has separate black and gray water tanks) as needed. Refill the fresh water tank(s) and use normally.
Drain the wastewater tank (if the RV has both black and gray water tanks, drain both). Make sure the drain valve is closed tightly when finished.
Fill a bucket with a gallon of hot water and add 2 cups water softener; stir until dissolved (by hand is fine).
Pour a small amount of the mixture down every drain (kitchen and bathroom sinks, bathtub) and the rest down the toilet. If the RV has separate black and gray water tanks, pour the entire mixture down the toilet, then repeat the process and pour the second bucket down the drains evenly. Use the water systems and toilet as you would normally. When the wastewater tank (or black water tank) is full, pour a cup of laundry detergent down the toilet; rinse the bowl, then drain the tank.
