As it often happens, the gallbladder releases the hard, calcified stones at the end when the liver is pretty clean and more bile is available for the gallbladder to force out these stones as well.
Your experience once again shows how important it is to cleanse the colon liver flushing, especially when calcified stones are involved (they are more likely to get caught). When doing a colonic the tender area of the anus is protected from the sharp edges of these rocks, thereby allowing them to come out without causing injury.
Well done, this should make a difference to any pain experiences that you may have had in the body.