Do you drain the hot water heater when winterizing?

It depends on weather you are planing to be living there or moving out for the winter and if you plan to be running the heat all winter. That said you should, if you do not plan to heat the house/camp all winter, drain all the water lines. This includes shutting off the water heater and draining it. Put anti freeze in all the drain traps including the toilet. Use the non toxic antifreeze!

Just wanted to add this.

Yes, if you want to winterize the unit, close off the water supply to the unit, open the release valve, then hopefully you can attach a hose to the bottom drain valve and drain the tank. Leave both valves open.

You don't want water sitting in the tank, not moving (refreshing itself) for long periods of time.