Keep Your Nitram Sharp... and the Charcoal Dust to a Minimum!
Take a paint stick and glue 220 grit sandpaper to both sides. When there is a lot of residue, simple turn the stick over and continue sharpening on the other side. This will cause the residue to fall into the container. Make sure that when sharpening you do not go past the edge of the container.
When you have a sharp point simply tap the stick on the edge of the container. This helps eliminate the dust around the container, and keep it out of the air!