Take the RV to a certified dump station at a campground or highway rest area. Dump the entire contents of the black water tank. Fill the black water tank 2/3s full of water and 1 cup of bleach. Add this through the toilet. Drive for five to 10 minutes, preferably on twisty roads where the water sloshes around in the tank. Drive back to the dump station and empty the tank again.
Drive to your home or parking area. Go to the black water tank housing -- typically in the rear right-hand side of the RV exterior. Open the panel and look inside to the tank itself. Wear your safety gear, including apron and gloves.
Fill a bucket with warm water and 1/4 cup of bleach. Dip a sponge or rag into the bucket and wipe around the top of the tank and unscrew the hose clamp on the intake hose. Pull the hose off the tank. You'll get some ooze from the hose, so be prepared. Slide the funnel into the tank and pour the remaining bleach water into the tank. Wipe down the hose and intake valve.
Fill the tank once more to 2/3s full and drive around again, letting the water slosh in the tank. Take the RV back to the dump station and drain the tank. The two washings with bleach typically clean the sensors.
