Can I use manuka honey to treat my chronic sinusitis? What is the recipe for the rinse? Thank you.

Yes. You can use manuka honey only if you have had surgery. Otherwise, the irrigation will not reach the sinus cavities... It will just run through the nose. The same for any nasal rinse. If you have had surgery, the sinus cavities are open to the nasal cavity and the rinse can get into the sinuses.
Honey nasal rinse. You can use honey, but studies show that adding a ten percent xylitol (sugar) to the nasal/sinus rinse is more effective. The bacteria take up the xylitol as it looks like regular sugar food to them, but xylitol weakens and kills the bacteria. When used as a mouth rinse ten percent xylitol solution also kills gum bacteria that causes cavities.