Flushing a water heater
I hook up a hose to the lower valve ; the other hose end is outside. I put a ball cock / 90 degree shut-off valve on the hose. Open the heater valve then open and close the ball cock at roughly 30 second intervals , the intent is to stir up sediment. Several cycles. Leave the gas and the inlet valves open. The burner will come on and the heat will help move sediment. It does waste hot water but should significantly extend heater life depending on your water. The objective is to remove sediment ; you change water every time you open a faucet. If you are limited to only a bucket , don't bother. Assuming a typical US domestic water heater; the inlet and outlets are at the top , fortunately the inlet has a pipe going to the bottom of the tank . This inlet and the burner coming on will tend to stir the sediment. Don't turn on any faucets while flushing, as you could mess them up with sediment. You could put the outside end of the hose in a bucket, it will catch some of the sediment and indicate progress.