Personally I see no problem with an occasional soak. They will hydrate through the skin and if there are humidity issues it will keep them hydrated. There are little to no down sides, just as long as the water is not too warm (88+) and it is not deeper than the 1/2 up the body of the snake.
mark and marley I have a small suggestion for the future rather than a sink buy a cheap 'dish pan' or any correctly sized flat bottomed container that way you don't get a deep spot the water can be an even depth.
Soaking before a shed however is not a great idea. It does not do what would be expected. The layer of liquid between the old and new skin is not water but a secretion and is slippery. It acts as a lubrication to the shedding skin a soak before the shed cycle washes away this lubrication and can lead to poor sheds. After an incomplete shed the secretion dries and a soak helps re-moisten the old skin and aids in removal. Snakes should not be soaked when 'blue'
r. Journal of Zoology, Alibardi, 246 pp 379-390