If I soak a bean, I use a small glass of warm water with a coupla drops of soap...sit it on germ mat 24 hours, then plant. I seldom let a bean sprout before planting... too much chance of damage to the tail.
Soap is an excellent way of softening/reducing surface tension and I even use a little soap to help nute uptake during veg.
That being said, after 14 years of growing, I now simply put a bean in moistened soil, cover, place on heat mat and wait.