Scott_G replied:

That small white plug will probably be a ceramic gas filter
Dust or other contaminants in the gas block the gas jet. Most gas appliances have a filter fitted. I had to fit a filter to my Coleman stove because the regulator that came with it kept getting small particles in and blocked it.

wal replied:

I think it is a great idea, the old chestcolds a pretty bullet proof, the only trouble I had with mine on our around oz trip, it got dust in the gas connection while we were up the cape. A good friend fixed it for me and since then I've used a plastic cap to cover the inlet when not conected to the bottle. The chap that helped me out used one strand of a wire fishing trace to clear the jet and also soked it in white spirit beforehand.
regards wal

Member - Oskar(Bris) replied:

And to stop hornets building mud-nests in the hole.
OskarThe real oskar