You resort to such a technique when the fire is particularly strong. But you use it only in the most extreme cases. With diarrhea, it's the same. In a severe case, you might have to fight diarrhea with diarrhea. But only in rare cases, and not as a routine method.
Diarrhea passes through the large intestines.
Below the large intestines, there is the rectum. The medicine that'll do the job would constrict the large intestines and reduce the fluid content. Don't try to memorize formulas. You have to try to understand, just using common sense, the basic principles behind the efficacy of medicines. Say, your child has diarrhea, and all you have available to administer to him are cheese and some charcoal.