h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I do that often - in the shower - much easier & cleaner (but do it before soaping!) and think maybe it keeps me reasonably clear, most of the time.
Perhaps it clears out the reservoir of infection in the mucus - but I've no evidence.

It started when I had to shovel coal & coke from a dumped pile into the coal house - on a regular basis. Black handkerchiefs!

I'm fairly sure it's been mentioned as part of a religious cleansing ritual (Islam perhaps - desert dust) but haven't found a reference.

I don't know about infections, normally they cause the mucus, don't they?

Certainly they cause irritation so increasing amounts but you need mucus anyway, to catch undesirables.

found something:

>Traditionally a neti pot, an Alladin’s lamp or tea pot shaped vessel, has been used to flow salt water into one nostril, through the sinus cavities and out the other nostril. In addition to using the neti pot, ancient yogis experienced success by snorting salt water in a rhythmic fashion as part of their daily rituals.<