If you already have water in the fresh water tank, leave it there and use the proper amount of bleach for a full tank and then fill it up. I remove my filter after I release the pressure on the lines by shutting off the pump and then open up a tap.. Run the bleached water through the water lines via your pump until you can smell the bleach in the water coming out of the taps, both hot and cold. Remember your outside shower. You can also just use the city water connection to clean your water lines and water heater only. Pour the required amount of bleach into a hose, connect to the trailer and run it into the water lines that way. Don't open up the taps until you're able to go to each one and wait for the bleach smell in the water. I usually let the water in the tank sit overnight before I flush it out with fresh water.