Your hot water heater accumulates sediment from your water source. If you don’t periodically flush the hot water heater, the sediment keeps building up which can cause the heater to work hard to heat the water, and it can cause damage to the tank and piping itself. It is important to flush out the hot water heater annually so that you can keep the sediment from accumulating in the hot water heater, thus keeping the unit lasting longer before a replacement is required.
For this maintenance tasks, you should really consult the owner’s manual for your specific hot water heater instructions. There are primarily either electric hot water heaters, or gas hot water heaters and there a number of safety precautions you should take depending on which one you have.
Your will need a garden hose as your primary tool for this task. You will need to connect the hose to a valve on the hot water heater and run it to an outside drain or to the front of your home.
Here is a summary overview of how to do it from the FIX IT Home Improvement Channel, but again, you should read the instructions for your specific brand.