How Does Mupirocin Ointment Help Control Or Stop The Clear, Water-like Drainage From My Sinus Infection?

I have a sinus infection that the doctor cut a portion of material out to allow for better drainage. Infection not cured, but my now continues to suddenly break out in a drainage. Doctor prescribed ointment Mupirocin 2%, swab twice daily for 2 weeks. I assume it is supposed to stop, or control the clear water-like drainage. In reading the possible side affects of the ointment, How does it stop the drainage?