Water heaters should be flushed every one to three years depending on the model and water source. Sediment buildup in the tank can reduce your water heater's energy efficiency and also clog your water lines. Avoid these problems and increase the life of your unit by flushing the tank.
How To Flush the Tank
Turn off the electricity to the water heater or turn off the gas to extinguish the pilot. Shut off the cold-water inlet to the water heater.
Connect a garden hose to the tank's drain valve. Locate the draining end of the hose in an area that won't be adversely affected by the scalding hot water.
With the pressure relief valve open, open the drain valve and allow the tank to drain completely. Completely draining the tank ensures that you've removed all of the sediment possible.
Close the tank drain valve, disconnect the hose from the valve and close the pressure relief valve. Open all the hot-water spigots in the house, and turn on the cold-water inlet to the tank.
Close each hot-water spigot as water begins to flow from it. After all the spigots are closed, turn on the electricity to the water heater, or turn the gas switch to run.