Drive the trailer or RV to a certified dump station. These are found at campgrounds or highway rest areas. Drain the black water tank at the dump station. Drive to your parking area and turn off the RV or trailer.
Mix one cup of bleach with three gallons of water in a bucket. Open the tan panel door -- typically on the rear-right side of the trailer or RV. Disconnect the hose from the toilet to the black water tank and place the funnel in the tan's valve. Pour the bleach-water mixture through the funnel and into the tank. Use the funnel so the bleach water touches the sides of the valve as it enters the tank.
Reconnect the hose to the toilet and turn on the water to the trailer. Pour water into the toilet and flush several times. Let the bleach water stay in the black water tank for several hours. Drive back to the dump station and drain the bleach water from the tank. This process sterilizes the tank.
Bring the trailer back home and park it. Pour two to three gallons of antifreeze in the toilet bowl and then flush the toilet. This puts antifreeze into the toilet, the hose and the black water tank, preventing freeze-ups during the winter months.
Add more antifreeze after each flush if using the trailer for winter camping. If the trailer is being put into storage for the winter, leave the anti-freeze in the tank.
