Your RV has two types of holding tanks: a gray water tank and a black water tank. The gray water tank holds water coming from the shower and sinks. The black water tank holds the wastewater from the toilet.
Simply emptying your tanks is not enough. Any buildup in the tanks will create blockages and unpleasant odors. A clean tank ensures the tank sensors work properly, giving you accurate readings of the contents and fullness of the tank.