Originally I ordered the Gardus LintEater at Amazon, and with it I pulled out three plastic shopping bags' worth of lint (!) that had accumulated over a period of more than 35 years in my condo unit. (I'm sure the pipe had never been cleaned.) This lint had been packed so tightly, I needed to work hard, bit by bit, with the little rotary chopping tool (included in the original kit) to make headway. It was a dirty, sweaty job, but effective in breaking very solid blockages. Further, the vent pipe run was longer than 12 ft. I compensated by running the LintEater in from both ends -- at the exterior vent opening, and at the dryer end. However, to my surprise, after completing this process, laundry drying time was still running way too long. That's when I ordered the extension kit, again via Amazon. The extension enabled me to run the brush all the way through, till it came out the other end. Doing this, I hit a lint blockage I had not been able to reach before. Another bag's worth of lint! At last I can dry a load of towels in one pass. Delighted. Note: I gave this product 5 stars because overall it worked outstandingly well. However, you should know that the Gardus LintEater works much better and the process goes faster if you work with a co-conspirator. You see, Gardus had to make the shafts flexible enough to work through 90-degree bends in vent pipes. But there's a tradeoff: with the drill running, lengths of 3-4 or more connected shaft segments quickly kink up before you feed them into the pipe. Working alone at first, I had to connect and disconnect shaft segments each time I ran deep into the vent, to avoid having too much loose shaft outside the pipe -- it would kink up. Very time-consuming. Later, having an assistant let me stand at the vent opening, feeding and guiding the shaft, while the other guy stood far away with the drill. By keeping the loose shaft straight, this arrangement generally prevented kinking. The whole process went at least 3x faster than my solo experience because I didn't have to assemble and disassemble sections each time I ran the thing in and out of the vent pipe. Another thing. The instructions caution you to wrap tape around each joint as you assemble the shaft segments. I spent a lot of time doing this, at first. However, later I omitted this step, which also saved time. However, if you do ignore this step, know that you run the risk of losing your shaft AND brush inside the pipe. This could be a very, very expensive problem to solve, thus I don't recommend it. I myself compensated for the added risk by tightening each joint with extreme care. Maybe I was just lucky, but it worked. Overall, very satisfied with this product.