Some people who have a colostomy or an ileostomy still have part or all of their rectum. The rectum is living tissue, and will continue to produce mucus. This mucus may leak out of the rectum at times, especially if it tends to be of a watery consistency.
Some gauze or a sanitary napkin worn in the undergarments may help to catch unexpected leaks. It may also help to periodically sit on the toilet to try to expel the mucus.
If the amount of mucus is excessive, particularly bothersome, has a foul odor, or is green or yellow in color, it may need to be investigated by a physician.Source:
Cancer Research UK. "Rectal leaking after colostomy surgery." NHS Information Partners 08 Feb 2007. 13 Jun 2012.