Draining a water heater takes 20 to 60 minutes depending on tank size and sediment accumulation. A standard 40-gallon tank drains in about 20 minutes through the drain valve. Heavy sediment can slow drainage significantly. Connect a garden hose to the drain valve and route to a floor drain or outside. Open the pressure relief valve to allow air in and speed drainage. Turn off power and cold water supply before starting the drain process.