Product review (5 stars): Gardus LintEater
I had not fully cleaned our dryer vent in over 30 years.  In some places, the build up was about 1/2 inch thick.  Working from both ends of the vent, the device along with a shop vac made short work of cleaning out about 20 feet of vent with three curves of from 45 to 90 degrees.  The only problem I had was with fitting the flexible rod's end into and out of my drill's 3/8 inch chuck.  I think a 1/2 chuck would be ideal.  A very good product for the money.