Funny, I have been using the hot water method for months now, and never have any of my vulcanite oxidized, nor has any of the wax melted. I think the water would have to be pretty darn hot. It has kept my pipes looking like new and smelling fresh.
But, even with water and reaming it with a paper towel after each smoke, I still get cake. And, while I don't recommend it to anyone, because most people can't even keep a blade sharp these days, much less handle a knife with delicacy nor precision, I gently slice the cake down to keep it evened out and down to a very thin layer. But, I work with my hands by trade, and not everyone has the finesse needed to be able to do this.