I have an ileostomy and have daily rectal mucus that is increasing. Had weekly mucus last year. How can I slow mucus production or stop it?

Not much. As long as your rectum remains, I will continue to produce mucous, just like yourmmouthmakes saliva.
Uncertain. I do not know why you had ileostomy surgery and what portion of your colon or rectum is remaining. If you have a large amount of colon remaining, it will naturally make mucous. If you had some form of colitis requiring the surgery, then colitis treatment may be indicated. Proctofoam enema could be an option. Best to see or ask your doctor.