Magnesium Anode rod. All Suburban RV Hot Water Systems have an anode rod which absorbs all the corrosiveaction of hot water. It is located on the bottom of HWS under the main burner. You simply unscrew this to drain the tank of water. If the rod is eaten away, replace it with a new one
CAUTION Make sure that the water in this unit is COLD Release the pressure before removing the Anode.Failure to do this may result in being burnt by hot water. If unsure or cannot understand what I mean please take your van to an authorised repairer.