RV glossary · Water & holding tanks
Black tank
Also called: Black water tank
The holding tank connected to the toilet. It is emptied at a dump station or sewer hookup, typically before the gray tank.
Use plenty of water when flushing and RV-safe toilet paper to avoid clogs and buildup. Keep the black valve closed at full-hookup sites until the tank is at least two-thirds full, then dump, so solids flush out with the liquid.
Many RVs have a black tank flush connection that sprays water inside the tank to rinse it after dumping.