If you have a good old one and the threads aren't fubar you can use a cutoff wheel or the like to slice and slit down vertically on the thread to cut them away and use that. It makes a gap in the threads to allow the shit to collect. Works in a pinch sometimes.
OR, get a nice thread chaser set, they aren't expensive. They might work better in some instances because you don't really want to be removing material, the chaser sort of just reforms the thread, and that's kind of the goal with that slit in the old spark plug idea.