I discovered by accident how well a P&B shake works directly after a flush. I got as many stones out via that as came out the next morning after the shake. Yes, the stones often get stuck to the mucoid plaque or whatever, in your intestines and frankly, they make for really stinky gas.
I always follow a flush up with a few P&B shakes now - you'll see parasites, eggs and stones both if you look carefully enough, all hanging out in your intestines, some directly from the gallbladder I think. Some of my gallstones looked quite old and must have been hanging out in the muck for awhile.