try calling one of Harmon's responsive customer tech reps at heath N home technologies
(that's a Joke for those of us who know Harmon)
anyway, creosote is dangerous to be sure... but assuming you had your chimney cleaned within the last few years (something you should do if your burning wood) and you have a good terra cotta liner and good chimney your probably worrying to much
when you have the chimney cleaned of course some of the flakes are going down your stove pipe where you will vac them out. if you had some photo's looking up and/or down the chimney we could see what kind of build up were talking about here... the major problems happen when this creosote builds up to thick levels of caked on cement (not just a few flaky flakes and a haze of black on the terra cotta)... your chimney (and many others) could have a fire in it without any problem what so ever (you might even be oblivious to its occurrence)... its when that creosote is so thick it turns into lava that pours downward into your living area where the major concern is!
I don't mean to make light of something that you should and are aware of and concerned with... I just don't want you loosing sleep if were only talking about a lil black haze and some flaky flakes. You have a great liner! (they build stoves, chimnias, ovens, black smithing blast furnaces, etc. out of terra cotta!)