Getting trouble with Water Heater Repair and Installation Flush the water heater tank: This should be done once a year. Start by turning off the electricity or gas to the heater. Then, close the valve supplying cold water. Connect a hose to the drain valve. Open the hot handle of any faucet and safely drain the tank. Once the tank is empty, close the drain valve and remove the hose. Then, you should open the cold water supply. Next, open the hot water faucets throughout your house one at a time, and wait until water flows out from them before restoring power to the heater.