The ones I had to give a good soak to (rescues, way back) I preferred to do it in a tub. Like a plastic tub, not the bath tub.
Water luke warm (check, what can feel luke warm to us, can be kind of high to them)
Water level not so high that they literally have to swim. Just high enough to cover their body. I prefer to put a towel in there, something they can rest on and slither through.
While snakes can swim well, usually, it can still be stressful to one to suddenly be submerged in water. Especially if that snake is not the healthiest to begin with and the temps are not quite right.