I don't typically clean any of my reptiles. If they have something stuck on them that I'm worried about causing a potential health issue (like they've crawled through poo and have it stuck to them) I usually just use a wet paper towel to get it off. I just make very sure to wash my hands well after doing anything in that room; even just touching the doorknob or checking the temps.

The main thing I'd worry about using any sort of chemical (especially soap or shampoo) in a soak or bath is the snake drinking it. It only takes a second of looking away for the snake to decide to take a sip. For that reason I never soak with any sort of chemical unless it's medically necessary. (I don't soak anyway, but a water soak can't potentially poison the snake lol).