If you have diarrhea and spill it on your couch, the best thing to do is clean it up immediately. Use a paper towel or cloth to blot up as much liquid as possible, then follow with a cleaner specifically designed for removing stains. For fabric couches, you may need to shampoo the area to remove all of the stain and odor. If your couch is leather, wipe it down with a damp cloth and mild soap, then dry thoroughly.