Maintaining your water heater can be a major factor in the number of years it stays working efficiently. A great way to maitain your unit is to drain it. While opinion may vary on how often you chose to drain your tank, you should try to always do it at least once a year.
Not sure how to get started on this? Below are step by step directions. Of course, if you don't feel comfortable doing this on your own it is never a bad idea to consult a professional before getting started or even to do the draining for you.
Shut off the water supply to your water heater
In most cases the water pipe and shut off valve will be located at the top of your unit. Turn the valve to shut off the water supply to the tank
Turn off the power to the water heater
If you have an electric water heater, turn off the power from the circuit breaker box. It is CRUCIAL to remember that if you fail to shut down the power to your electric water heater you risk burning the element out. If you have a gas water heater shut off the gas by turning the valve on the gas supply line that runs to the tank.
Give the water some time to cool off
Because this is a water HEATER the water is going to be extremely hot. To prevent any kind of injury it is best to let your water heater sit overnight to allow the water to become cool before your drain it.
Attach a hose to the drain valve
Once you have given your heater time to cool off place one end of the hose into a floor drain or outside if you find the hose will reach. Attach the other end of the hose onto the drain valve at the bottom of the water heater.
Turn on the hot water tap
Turn on a hot water tap at a sink that is closest to your water heater. This will help alleviate pressure.
Open the drain valve
Opening this valve will cause the water to begin flowing out of the tank. Draining the water can take up to 30 minutes but is dependent on how full and dirty the water heater is.
Turn the water back on to flush the tank with fresh, clean water
While the drain valve is still open, turn the water back on to eliminate and remaining sediment. Once the water is running clear you can turn the water valve off.
Refill the tank
Remove the hose from the drain valve and turn the water back on. Start refilling the tank. Leave a hot water tap/faucet open to allow all the air from the tank to leave the system. Once clean water rund out of the tap, the heater is full and flushed. Now is i full and you can turn the power to the water heater back on.
source for DIY tank draining from :https://blog.allstate.com/tips-maintaining-water-heater/?pgv=c