I've just heard of bathing if your corn isn't shedding all in one piece which means the humidity of the viv hasn't been high enough. However, if your corn slides through his or her poop, a bath might be necessary based on owner preference for handling clean smelling snakes.
For my 2002 hatchling, Lava, though we found that stoppering the tub and putting just a little warm water in it was too frightening. It was too big of a space. It would work well for a larger corn, though, I'm guessing. A shallow appropriate size container of warm water, not too deep, will work. Some corns routinely bathe in their water dish, which is why they tell you to buy a large water dish.