Most nutrients are absorbed in the duodenum and small intestine. The colon helps with electrolytes and helps with undigested food...fiber etc...
25 pounds of impacted matter in the colon? I would get a colonoscopy before i would assume that there is that much impacted matter in the colon.
I dont know of betonite clay to "pull" matter off the colon walls. There is nothing chemically in betonite clay to cause the colon to contract and expand. I have heard of betonite clay to "absorb" some toxins.
Its interesting how some websites say that green rubbery garbage can be the buildup of psyllium/chrolophyll/clay in the intestines that is getting lodged . Just something to be cautious about.