Good day Doctor. My question is couched in my personal observation from time to time, after my bowel movement, that there appears in the bottom of the white porcelain bowl after flushing, a dark, sandy (grity) substance which continues to peak my curiousity? I am 72 years old, 210 lbs., in good health, with the exception of higherer cholesterol levels than I would like (but I am on Simvastatin to keep it in check). and I take two different prescription meds to control my acid reflux.