There should be a plastic pipe coming down from the tank bottom. On most it's relatively small (1/2" pipe) Empty would be my preferred option.
If you don't drain it, you do want to put in antifreeze but it will take a good amount to dilute the water in the tank and then you will have to fill and drain several times in the spring to get the taste out.
Our current trailer has a really nice setup. They fit it from the factory with a 1.5inch blade valve (similar to the gray water drain but white and clearly labeled for fresh water use). A quick pull of the handle and the fresh water tank quickly drains with no tools needed.