Very few people who flush normally gets stones out from just taking the Epsom Salts . Sometimes people get relief from a single dose of Epsom Salt during an acute attack.
And in the Hulda Clark book she says that the Epsom Salts are to dilate the biliary tree so that the oil can do its job. If the Epsom Salts were the main stimulant then there would be no need to drink the oil.
The oil is what provides the proper stimulation for contraction.
Also, before the flush was a thing and in books, hippies were doing them in the 60's without epsom salts and they worked fine.
Mind you I don't think anything I said contradicts the study. I was guessing at which components do what, and I was aware of this study, or another one similar to it, previous to your post.
The grapefruit/lemon/whatever's purpose is just to make the oil go down easier. People do fine with plain oil (the ones who can tolerate this). And the Sutter coca cola / oil flush works as well or better than with grapefruit.
Further, the Hulda Clark instructions are to take 2 more doses of Epsom Salt the following day to clear the bowels not to stimulate bile flow. If the purpose was to keep pumping the gallbladder then there would be no reason to restrict fats the following day.
In any case it's neither here nor there. I've done tons in all ways and magnesium glycinate is superior. There is no stress on the gut, no diarrhea, no electrolyte loss, the relaxation is better because you're actually absorbing the magnesium instead of squirting it out your bum. A lot of people fear doing the flushes because they don't want to suffer the epsom salts.
Beyond that, the more important issue is to not have to do flushes, so beets, taurine, tudca, diet, detox, deparasite, etc. Endless harsh flushing with epsom salts is not what anyone wants.
To beat a dead horse because it's important and people lose sight of this in flushworld: the most important thing to go after is solubility. The flushes are a stopgap measure to force things out mechanically and do not address any underlying chemistry.