I've only ever had to use something twice, to get a snake to release. Once my adult female Rosy boa mistook my hand for a mouse and clamped on and started to constrict, pouring room temp water over her got her to release almost immediately. Then my husband got bit by Kaylee, our adult female BRB, the largest snake we currently have, and water did not work on her! It was a very painful bite because she grabbed a chunk of the flesh on his arm, pulled it out and then kept trying to twist it, he was afraid it was going to tear at any moment. So I poured mouth wash in her mouth and she let go immediately. She was very pissed off about it too. Not something I'd recommend for the first thing to try, but it is always effective if you can't get one off any other way.
Like I said, it was very painful but only because of the way she was twisting his skin, the actual punctures were like a moderately bad cat scratch and didn't hurt much after she let go.