There is no need to soak overnight - since it's on the back of the neck if you soak the snake - that part of it will most likely be what he keeps out of the water.
Soak for about 10 minutes in luke warm water - this may not remove the skin completely but it will aid in loosening it - make sure its only deep enough that your snake can comfortable rest on the bottom without having to swim the whole time.
Take snake out and put in warm, damp towel and wrap him up. Most snakes will just sit inside without hassle. After about 5 minutes in the towel encourage your snake to wiggle around inside. The movement through the course towel should be enough to slough the skin right off - if not you can wipe it a bit with a corner of the wet towel.
Most balls find soaking rather stressful so you don't want to rely on soaking as a shed aid - don't over soak either - ironically it will dehydrate your ball and could lead to an RI.
When it's all said and done - a little remaining shed is not a big deal - it can remain safely on the snake until the next shed.
good luck!
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Tosha 
JET Pythons
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