What's the best treatment to get rid of black stools?

Determine cause. Black stools could be due to iron supplements, bismuth antidiarrheal agent (e.g. Pepto bismol), or bleeding from the upper gastrointestinal tract or sometimes right side of the colon. Bleeding can cause black, sticky, smelly bowel movements. If not taking iron or busmuth, or it continues after stopping, it really is necessary to get seen and be sure there is not a serious but treatable cause..
See a doctor. Black stools are concerning for occult bleeding in your upper intestines. See a GI doc for further evaluation.