Draining the hot water heater?

I just read that one way to save on the heating bill is to drain the water heater once a year so that sediments do not build up and make it less efficient. My question is whether it would save a lot of work to just turn down the temperature a little for about a week. That way, the water heater gets depleted... show more I just read that one way to save on the heating bill is to drain the water heater once a year so that sediments do not build up and make it less efficient.

My question is whether it would save a lot of work to just turn down the temperature a little for about a week. That way, the water heater gets depleted naturally as we use up the hot water every night. As the hot water stored in the heater gets used up, it is replaced by cleaner, cold water. After a few days, I could restore the higher temperature.

Does it make sense? The water heater is gas, and it is around 20 years old. Not broken, but not rusted through or leaking so that it doesn't need to be replaced just yet. Thanks.
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