To drain a hot water heater, first flush the system with full water pressure. Connect the drain hose and open the drain valve briefly before shutting it off again. Any sediment lodged in the valve will be dislodged, helping the system to drain more quickly. Next, shut off your water heater by disconnecting it from the gas or electric power supply, and turn off the main water supply. Then, with the drain hose still connected from your quick flush, open the drain valve. You won’t see much water flowing out until you allow air into the tank. To do so, you’ll have to disconnect the hot water pipe at the top of your water heater and move it to the side. The tank will begin to drain. Once your water heater tank is drained, flush it with fresh water.