Rance in the past I have just used a steam cleaner, set the tank in the upright position, put the steam cleaner wand into the tank filler neck, tie the handle to keep it open & let it run for 45 minutes to an hour or when the tank gets hot and the water looks clean coming out of the filler neck. shut off the steam cleaner and dump the tank out, remove as much water as you can . The heat should pretty well dry the rest of the water out
