you're absolutely correct. Sinuses are mucous membranes and so there is candida and other microbes living there. :)
I think that's why so many times Antibiotics don't do anything for sinus infections - they attack bacteria, but not fungals. :(
Sometimes the best thing is to snort some salted water. One of Ayurvedic medicine's techniques is to massage the inside of the nose with good sesame oil or Ghee. I've tried it once or twice, really helps with headaches and releasing emotions. :)
the other thing that contributes to clogged ears is a high-fat diet, or a clogged liver that is unable to deal with the fats you're giving it, usually dairy fats. So if you have a lot of ear discharge etc., keep on liver flushing! :)