+1 on both MSO and Mikes's suggestions--two different methods of achieving much the same thing. I scour the bowl with a folded over pipe cleaner after every smoke. This ensures a very slow buildup of cake. MSO's method is similar, except that it's far more aggressive, meaning that any cake will build up at an infinitesimal rate. I prefer to have a bit more cake, so I'll settle for reaming on occasion. However, you can teach an old dog new tricks, and I'm going to follow Mike's advice: ream cautiously and slightly, and complete the task with fine sandpaper. That way you'll never have to worry about chunks breaking off. I did such a lousy reaming job some thirty or so years ago that I had to take the pipe down to bare wood. What an awful taste that was. Not certain that I or the pipe ever recovered from it.
Anyway, you've been exposed to two different techniques, both effective. Pick your poison.