Unless you have frank pus coming from your nose, it's likely that what you're feeling is not a true sinus infection, but a variation of a migraine in your sinuses, due to the pressure irritation from CPAP. This can give you sinus pain, pressure, post-nasal drip and congestion. Did you ever try using a Neti-pot or any other saline irrigation system nightly?
I wash my humidiifier box both the plastic top and the alluminum bottom, my 6 foot hose and my face mask in my bathroom sink with Ajax Dishwashing soap and hot well warm water then everything is taken apart. I lay a towell on my bed and lay the peices on it and let them air dry befor I put this back to gether. JL