I expelled tons of it years ago in a series of 3 ultimate fasts I did. Taking P&B shakes for like 10 days while in master cleanse or juice fasting is to me one of the most effective ways to deeply cleanse the bowel. Every day after the salt water flush you expel these rubbery ropes that's just the Bentonite you've drank, impregnated with toxins like a sponge, it's like cleaning a bottle. The ropes smell even worse that they look! at least in my case, and I've never been constipated.
Better if you hydrate the Bentonite well before ingesting it, that is you put it in water for a couple of days to give it time to absorb all the water it needs, so that it doesn't take it from the body.