Good point, Aubrey! had not factored that into the equation! Ducks are very oily on their feathers.
All I know is I DONT clean mine and they do fine and if it aint broke I aint fixing it!
Good luck hatching!!!!
Here's my 2 cents worth. I would tend to think washing them off or spritzing them with water is no different than momma duck taking a swim on the pond and coming back to the nest to douse the eggs with water from her bumm. And believe me, they have a lot of water stored up there in that duck...