how to open up mouthpiece slit?

[andmer]

Hey All,
I want to open up the lip end slit on a vulcanite mouthpiece, I cannot get any sort of cleaner through it from either end, its VERY tight.
What would be a good way to do it? a mm or so. A file of some sort?
Recommendation needed! New pipesman.

 

[anglesey]

I'd get a flat file then some very fine sandpaper wrapped round an ice cream stick.