You get both primary and secondary enteroliths when liver-flushing. The primary enteroliths which I think you call "soap stones" are formed becasue the bile moves quickly from a acid envoronment to a very alkali environment in the ilium caused by the Epsom Salts . This enables the bile to precipitate rather that get cycled.
It takes two weeks to reestablish the chemical balance of the bile after a flush. So bile salts responsible for stopping bile from becoming sticky are the last to be replenished.