I drained mine last fall and we literally just opened the tap on the bottom. Closing the cold water supply, shutting of the gas/electricity should be done when those are operational. If they aren’t, that’s not a problem. The electric is as easy as flipping a breaker. The gas shutoff is a valve turn. Yes, as part of regular maintenance, you should drain your water heater once a year to remove any sediment from around the element. It helps the element stay cleaner and working happily. However, if you have a “gunky” hot water heater, it is sediment from your water supply, which I presume is potable, and something that you can filter with a cloth if you need the water.