I also have sinus problems that affect my diving. It used to get quite bad as my sinuses fill up with blood when I try to "force" a dive and push through the pain and blockage to go deeper - which is not a good idea.
Sometimes, I would come up on the surface after being in the water a while and suddenly expel a huge amount of mucous from my nose / mouth and then my sinuses would be fine for a while.
So far, my best solution to avoid sinus pressure/clogging has been targeting what causes the mucous build up in the first place. In my case, its has to do with diet and avoiding all types of dairy - anything from a cow except beef and organs. Even a little cream with coffee - I now use Soymilk. If I get a cheese craving - I eat a little goat cheese. I avoid wheats and processed flours - most breads, muffins, bagels, pastas, etc. This regimen really alleviates the build up. I also try eating lots of fresh fruits and veggies and stay away from junkfood. I try to stay away from drugs and I used to eat EVERYTHING in the past and never had any allergies either, but my sinuses always bugged me.
From what my doctor (naturopathic) told me, unless I have some kind of physical problem with my sinuses, my diet is the main contributing factor to sinus buildup.
