Turn off the water heater power at the breaker or set the gas control to pilot/off
Turn off the cold water supply valve to the heater
Let the water cool if possible
Connect a garden hose to the drain valve at the bottom of the tank
Run the other end of the hose to a safe drain location
Open a hot water faucet in the house to relieve pressure
Open the drain valve on the water heater
Open the temperature and pressure relief valve if needed to help air enter the tank
Allow the tank to drain completely
Flush sediment by briefly turning the cold water supply on and off if desired
Close the drain valve
Remove the hose
Close the hot water faucet
Reopen the cold water supply valve
Open a hot water faucet until water flows steadily to purge air
Restore power or relight the gas heater according to the manufacturer instructions