That is called muciod plaque. It is just a build-up of fecal matter in the colon. This junk will build up much like grease builds up in the kitchen sink drain pipe. A combination of psyllium and cascara sagrada will get rid of it.
The cascara sagrada stimulates the long muscles along the colon to work in a wave-like action. This loosens up any build-up - then the psyllium swells up in the colon and "traps" parasites, toxins and loosened plaque.
One of the first signs of plaque is a small diameter sized stool. The stool passes through the plaque much like passing through the hole in a doughnut.