Product review (4 stars): Works!
They say in the dirctions to run the cord with the Ductsmart from the outside of the house to the dryer vent that is disconnected from dryer.  Install the largest bush for the 4 inch vent pipe and then pull it straight out while the dryer is running.  I left the dryer running for fifteen minutes to dry the vent further.

I cleaned vent pipe with one pass that hadn't been cleaned in four years.  It was really easy to use.

I believe that with some of the smaller brushes that comes with the kit you could try turning the crank but it would have to be a looser fit than with the largest 4 inch brush.  I did try to crank the cord a little bit and all it did was knot it up instead of turning the brush.  So don't try to mess with the cranking feature of this device is my best advice.

It paid for it self and I know the job was done right.