If in use, you should dump your black water tank whenever your tank sensors read three quarters full. You should also dump your black water tank before storing your RV for any period of time. If you are staying at a campsite with sewer hookups, make sure to dump the tank, complete a black tank flush if possible, and add water and chemical to the tank before departing. If you are staying at a campground without sewer hookups, look for a dump station to empty the black water tank before you leave. If no sewer hookup or dump station is available, search for a place to empty the tank along your route. Pilot/Flying Js, state park campgrounds, and some municipalities offer the service for a fee.