The RV holding tank is the storage tank on your RV that holds the waste from your restroom. Some people do not allow solid waste on their RV and insist that a bag be used and then discarded. Your RV holding tank has a sensor on it that will let you know when it is time to empty the tank. Once the holding tank sensor has gone off, you need to dump your holding tank before using it again. If you do not have a sensor on your holding tank, or your sensor is not operating, then it would be advisable to empty the tank once every two weeks during peak usage.