If its not vaginal calmoseptine does wonders. I'm not sure what to do for a vaginal fistula. If you don't have calmoseptine I would try some other barrier ointment but calmoseptine is the best.

Agree with the calmoseptine. It also helps to "contain" the drainage. I don't know where your fistula exits, but you might try covering it with a cotton round or gauze. This gets changed after every BM.