Absorbs the corrosive action caused by hot water and prolongs the life of your water heater tank. Simply unscrew the anode rod to drain the tank. If the rod is mostly eaten away, replace with a new one. Always keep a spare in your RV toolbox. Magnesium rod is suitable for most areas. Consider using the aluminum road in areas of harsh waer where the magnesium rods last less than one year. 1/card.