On my 165 Sport, I do not have a drain for the fresh water tank.
I use the pump to drain most of the water. I will always have some left.
Many people say once you get it as low as possible, there's room for expansion and freezing is not a problem.
You can also add some anti-freeze in the fresh water fill spout, then flush in Spring.
I always put about 1/4 cup of clorox in my fresh water tank after using it, because there is always an inch of water left.
2016 Toyota Tundra SR5, 5.7 V8