I don't believe in the bloom theory. My hatch rate with unwashed eggs is 12% lower than they ones I wash in hot water right before putting them in the 'bator. My experiment lasted through the first 200 eggs, now I wash them all. I think that preheating them helps and it is easier on the 'bator since it doesn't have to warm them up so much (I do staggered hatches, hatching on most Mondays).