To drain a GSW heater, turn off the electricity or gas supply to the heater, then turn off its cold water supply. Connect a hose to the drain valve and direct it to a drain. Open a nearby hot water faucet, then open the drain valve to drain the tank.
Use the manual gas shut-off valve to turn off the gas on a gas-fired heater, or turn off the electicity at the breaker on an electric heater. This is critical for a GSW heater since the electric elements are liable to burn out if operated in a waterless tank. Turn off the cold-water inlet valve. Connect a hose to the heater's drain valve and direct it to a floor drain.
Open a hot water faucet nearby to let air into the tank and speed up the flow of water once the draining process begins. Open the drain valve and allow the water to flow out of the hose until it is no longer discoloured. Once the water runs clear, close the drain valve, turn the cold water supply back on and restart the heater.
Drain and flush a water heater every six month to remove any sediment that may build up during operation. It is also recommended to drain the water heater if it's being shut down for an extended period of time.