Sediments collect at the bottom of the water heater, depending on how hard the water flows through pipes. However, when you flush out the water heater, the drain valve will not drain bigger particles. Also, you are advised not to flush out the water heater on your own as, when draining, sediment may enter the rubber seal preventing the drainpipe from proper closure. In such a case, your valve may leak, so it’s recommended to get professional assistance.