Step 1: Materials list
1 ea. - 5/16" x 6' all thread
1 ea. - table leg mounting bracket,
2 ea. - 5/16" nuts,
1 ea. - fender washer,
weed eater line.
To make this simple chimney flail I bought a 6' length of 5/16" threaded rod at Home Depot for around $6.00. I found the table leg bracket at the Habitat for Humanity RESTORE and paid a quarter for it. The rest of the materials were on hand in my garage. I call it the cheap sweep.
Chuck the rod into a portable drill and head up to the chimney. Run the flail up and down the chimney pipe a few times. For a long flue you could use a 5/16" coupler nut and another length of all thread. My chimney was just around 6' from the top to the dampener so I didn't need a longer tool.
For a really dirty chimney I think you could replace the weed eater line with some steel aircraft cable.
I was amazed at what a wonderful job this did on my chimney but couldn't find a camera to show before and after photos.
Build one and give it a try, I'm sure you'll be happy with the results.