Boiled water works well, I recommend distilled because it's easier, with no irritating chemicals like my local water supply.
What I said is that "some" people have it as a result of sinusitis. I have had a horrible smell in my nose with no other symptoms, although I don't know that other people could smell it, and I removed it with a sinus flush. Some other people had a smell that other people could smell, and found out they had a blockage in their sinuses, like a cyst, that caused sinusitis pockets.
However, there are many people who have the horrible smell, have been to many many doctors, with no luck. If you do a sinus flush with no results after a week, then you are possibly in their group. Here is their thread, from the Respiratory Forum:
http://www.medhelp.org/posts/Respiratory-Disorders/Bad-smell-coming-from-noseFound-a-Cure-Yayyyy/show/520721