To drain a water heater, turn off its gas valve or electrical power, and then turn off its cold water inlet. Connect a hose to the heater's drain valve and open one hot water faucet in the house. Open the drain valve until the water from it runs clear.
Before draining a water heater, it's critical to turn off the power at the breaker box for an electric heater or turn off the gas valve for a gas heater. Alternatively, one can set the gas heater thermostat to Pilot mode. Turn off the cold water inlet of the heater and attach a hose to the drain valve located at the bottom of the heater. Run the open end of the hose to an outside driveway or a drain.
Open the hot water faucet on one of the sinks or tubs in your house to prevent a vacuum from forming in the plumbing lines once the drain valve is opened. Open the drain valve of your heater and observe the water pouring out of the hose. Close the drain valve and the hot water faucet once the water runs clear. Turn the heater's cold water inlet back on to refill the tank and then turn the electricity or gas valve back on.