I just ran a poly brush through the chimney and it never looks really clean to me. You can see the thimble opening in the lower part of the picture where I clean using a bronze BBQ brush and it looks nice and clean. The rest looks like it could be better. The brush isn't that old and never used on a warm chimney. I also turn the brush as I go so I don't see why it doesn't do a better job. Am I being too critical about how clean is clean?
http://i1006.photobucket.com/albums/af188/surfnet7/009.jpg
http://i1006.photobucket.com/albums/af188/surfnet7/009.jpg