Product review (5 stars): Does The Job!
Outstanding, well made product.  I have a 15 ft. dryer exhaust duct made of heavy foil "accordian".  It's a straight run from the dryer wall to the outside of the house at near ground level except for a 90 deg "S" bend where the duct enters the wall and continues below the floor next to the basement ceiling

Since the total length of the rods is 12 feet, I had to clean the duct from both the outside and inside.  After reading all the options in the user manual I concluded that the most efficient cleaning method was the following general procedure.  I ran the brush through the duct from the outside (while keeping the dryer connected to the duct) and then turned on the dryer on the unheated air flow setting to blow out the debris through the louvered outside vent that the brush did not extract.  Then I disconnected the duct from the dryer to the wall and ran the brush through the duct from the inside...being careful to allow the flexible line to let the brush negotiate the two 90 deg bends.  I reconnected the dryer to the duct and again turned it on air flow to blow the debris out the outside louvered vent that the brush didn't remove.

DETAILS: When cleaning from the outside, I attached the brush to one 3-ft. rod and attached it to my drill.  It's best to have a two speed drill (set at the low speed) or a variable speed drill.  The outside vent is plastic with three flexible louvers which are easy to remove.  I inserted the brush into the end of the duct, turned it on, slowly worked the brush into the duct the full length of the rod, and slowly withdrew the rotating brush (and watched all the debris being pulled out).  I did that three times. I then turned on the dryer (unheated air flow) to "clear" the duct.  After that I rotated the brush again into the duct to near the end of the rod, disconnected it from the drill, attached the second rod and repeated the process.  I reinserted the brush to near the end of the second rod, disconnected it from the drill, attached the third rod and repeated the process....etc... until I had all four rods (12 ft.) attached.  When I finished cleaning from the outside, I cleaned the duct from the inside, but I just needed to use one 3-ft. rod. to ensure the entire 15 ft run was cleaned.  Of course, don't forget to clean out the duct that connects to the  dryer.  I also opened the back of the dryer and cleaned the inside.  The debris sitting on the grass below the louvered vent was easily cleaned with a house vac using the suction tool.

Be patient, read the instructions and pay close attention to what it says about connecting and securing the rod sections.  Also, wear a good quality dust mask and hat.  If you have a long duct like mine, don't connect all four rods at once and then try to insert the brush and run the drill from 12 feet away -- it'll be too unwieldy.  Simply start with one 3-ft rod and add the additional ones to the rods that are inserted in the duct and protruding from the opening as described above and continue rotating the brush.  Push the brush in slowly and let it do the work; don't force it.  If you apply a little common sense it's really very simple.  But the whole cleaning process will take a long time, especially if you have to also clean from the inside which requires moving the dryer, disconnecting the duct and other contortions...so be patient.  It's a well-made, effective tool that really does the job.