The RV holding tank are the storage tanks on your RV that hold the used shower and sink water as well as waste from the restroom. Your RV holding tank comes equipped with a sensor that will alert you as to when it is time to dump the tank. Do not use your water facilities once your holding tank sensor has gone off. You should dump the tank immediately to prevent damage to your RV and to eliminate the odors that can accumulate. For older RVs without sensors, plan on dumping both storage tanks at least once every week.