Similar to a Crop Duster, but different in that a Must Duster always leaves behind a musty smell, like old mold, or like a dusty gust of penicillin spores fresh off an expired loaf of bread, but instead out of the Must Duster's rear.
Our office Must Duster walked by and sprinkled us with her moldy dust, thus creating a psynchronized nose covering to block out the spores of her un-welcomed scent.