Although dust and rust from the pipe is possible, much more likely is a black sludge building up in the tiny jet hole.
The sludge is condensate of the chemical added to the gas to give it a smell. It's also the stuff that ruins the regulator if the inlet pipe runs downhill into the regulator
The best way to clean the jet is to put it in an ultrasonic cleaner, but if you're on the road, that's not going to be possible.
Next best is to blast it through with liquid gas from a lighter refill. Be VERY careful to do this where the jet can't blow out of your grasp and vanish into the shrubbery.
Sometimes the jet is a domed metal plate/washer, but on my fridges it has always been a screw-in brass fitting.