One way to do this is to fast; no food in, food out. Another quick way is to use coffee enemas
, but fast means it can be dehydrating and should be done only under the care of a professional. To do on your own, find a product based on things such as psyllium and other fibers, which will gently scrape the digestive system walls. Some of these contain laxatives, which work faster, but shouldn't be taken for very long, such as cascara sagrada, aloe herb (not the juice), and butterbur.