Sometimes there can be a buildup of cake at the very bottom of the bowl which can block the draft hole. And, it might be too thick or stubborn to remove with a pipe cleaner. I use the rounded tip of the knife to remove it by scraping it in a vertical motion, followed by a pipe cleaner. If the pipe cleaner won't get through I use a piece of coat hanger about 6" long and folded to make a handle, to push any goop out of the draft hole and into the bowl for removal.I'm a little confused on how reaming the chamber walls clears blockages. I just run a pipe cleaner down the draft. YMMV
But, when I do need to ream, I just use a very sharp knife, but after being here a while I decline to suggest this type of thing to folks, because it does take a certain amount of skill to use.