I've had a bowel to vaginal fistula, this was when I was really very ill and also had a bowel to bladder fistula too. After a long surgery to remove some bowel, my surgeons decided to leave the fistula track
open to drain any nastiness away. While having an ileostomy in situ that fistula closed on its own thankfully. Previously for me remicade has healed perianal fistulas.
I'm sorry it's not exactly the same as your experience with a pouch but wanted to send hugs.