I use an even older-fashioned treatment than Dan's suggestion. I used to be plagued by perianal (and vaginal) fistulas, and each time, I would hot compress the area three to four times a day, each time for about 10 minutes. All I would do is get a piece of flannel (a facecloth would do just as well) and a bowl of really really hot water and use the hot flannel cloth to press against the fistula. I would also call my GI and go on a 14 day cycle of antibiotics. These two things would basically fix my fistula right up (until the next one, of course). A sitz bath might also provide some relief.
Cheers,
Kismet