When I let a snake soak I use a locking tub and it has no other place to go. If Im soaking them its for a reason so they need to stay in the water.
One other thing is when you soak them you don't want to leave them in water so deep they have to continually swim to stay above the water. Snakes can and do drown. I only put enough water to go about 3/4 of the way up the snakes body.