I have used both CS, and H202 in my sinus cavities, but never together. CS alone should take care of any problems you might have. The best way to get it into the sinus cavities is as a mist rather than a flush. I haven't had any pain when misting. I have a device made especially for the nasal cavity call the Allefree. Here's a picture of it. http://tinyurl.com/erja5
I quit doing H202 at the advice of a doctor that did surgery on my sinuses. She claimed that H202 removes the top layer of protection that forms in the sinus cavities naturally to protect them. I had always used a couple of tablespoons in about 10 oz of distilled water with Sea Salt . Never use tap water, or salt from the super market. Always use medical grade H202. You can buy 35% H202 here, and dilute it 1 oz to 11 oz of distilled water for your 3% solution. http://tinyurl.com/4taxn
The way I got rid of my sinus problems was to have all the Amalgam fillings I had replaced with composite fillings, and to have the root canals that I had removed. I suggest if you have any of this in your mouth that you do the same. Go to a holistic dentist.
I do the CS misting just to keep from having colds and other bacteria, or viruses in my sinuses.