Sediment build-up displaces water and prevents the heater from operating at full capacity. By flushing the tank once a year, usually before winter, you won't be wasting cash by heating this gunk. Start by turning off the heater and letting the tank cool; then shut off the water supply. If gravity is on your side, connect a hose to the drain cock and run it to a floor drain. If you don't have a drain, send the water to a sink or bucket using a drill pump (a $15 attachment that will suction water out of the heater). Draining 3 gallons is usually enough, but you may have to fill and flush a few times until the water's clear.