You're probably thinking of the fact that some people use bathes to help aid a constipated corn in defecating. However snakes don't poo very often so unless the lump in his belly has been gone for quite some time, and he still hasn't used the bathroom, then a bath isn't really needed.
Baths are good for helping a corn shed, and to help a constipated corn, but I think baths for any other reason will probably stress the corn much more then needed as a lot of snakes seem to not enjoy it too much and try to escape.
It's also important to make sure the temperature of the water is right. I would only use water that's between 75-78 degrees to be safe (my personal thought here) and water at this temperature feels very cool to us as our body temperature is in the high 90's. So if you're giving him a bath its best to use a thermometer to check the temps before you actually put your snake in