If you can find your water heater, then you can flush it without any specialized training, according to This Old House. Their website features a short video demonstration of the flushing process. Several other videos can be found on YouTube that demonstrate this process.
Iron deposits from plumbing and other material will accumulate at the bottom of a water heater tank over time. Regularly flushing a water heater tank is essential to keeping the hot water in a house free of sediment.
Flushing a water heater is an extremely simple operation, requiring only a hose and a place for the water to go. If there is no floor drain lower than the heater tank, a small pump may be necessary to pump the excess water to a drain or outside.
After turning off the electricity to the heater or turning the gas to its lowest setting, the water to the tank is turned off and the tank allowed to drain from the spigot located near the bottom of the heater. The tank is then refilled and drained again until the water coming out of the heater is clear. Depending on the amount of sediment in the bottom of the tank, this step may have to be repeated. When the water flowing out of the tank is clear, the heater can be refilled and turned back on.