The amount of bile produced in a flush lubricates the bile ducts, while Epsom Salts dilate them. This doesn't happen during a gallbladder attack. That's why taking a Tbsp. Epsom Salts when in the middle of an attack is the recommended way of halting the attack and pain. Moreover for a flush there's also been sufficient previous stone softening and crushing. Even the proponents of those protocols that don't use Epsoms (like Julia Chang's) don't worry much for stuck stones 'cause the pain sensation is much milder than during an attack and in those rare cases their tinctures can push or soften the stuck stone.
Most people report gallbladder attacks disappearing completely after just their first flush. That's even before the calcified stones at the bottom of the gallbladder have started coming out. They usually start coming out after 5 flushes. These stones sink in the toilet water, they're not the bright-green oily type. They can be spotted because the laxative effects of Epsom Salts make sure that no fecal matter obstructs the view. Collect them to feel they're really stone-hard. A hammer blow may break them apart. Huge sizes have been reported, up to 3 inches across. From the beginning this forum has witnessed links to sporadic unorthodox opinions by M.D.s who've come to accept that stones can exit the gallbladder with these methods -like they do in a gallbladder attack, only without the pain and spasms-, and also reports from people who've taken ultrasound scans as confirmation.