It's hard to say for sure without a picture, but the clay/fiber is taking out little bits of undigested food particles, which can look like just about anything you can imagine, and possibly yeast overgrowth or even the larger parasites or their egg sacs/nests.
Mucoid placque is a combination of undigested food particles and the lining of the intestines. If it's newer and softer, it will break up and come out in little pieces. If it's older and tougher, it'll come out like strips of tire tread!
Isn't it nice to know that stuff is OUT of you? Better out than in as they say!!! :)