Product review (5 stars): 48 ft - It worked
I bought 4 kits, screwed 24 sections together, wrapped joints in duct tape to prevent unscrewing, forced the brush through over 45 feet of metal dryer exhaust pipe (with 180,90,90 bends) and spun it with a drill.  I cannot believe it worked as well as it did; I was not gentle.  Out came a small mountain of wet lint.  I ran it through both the interior end and exterior end of the vent pipe several times (which was approx. 55 ft long).  Dryer works great now.  Highly recommended!!