Product review (5 stars): This did the trick for me. Use your leaf blower to test air flow afterward.
Love this thing! No, it won't navigate super sharp turns, but there are ways to work around that as long as you only have one super sharp turn. I was only able to go two feet from inside the house, but was able to go ten feet from outside, and pulled out a TON of sludge and dirty water. I was expecting dry lint, but apparently the steam can get trapped enough to collect a lot of water as well. After I was no longer able to pull anything out from outside, I used a leaf blower from inside. The dryer repair guy told me to cut a hole in the end of a garbage bag, and tape the bag to the leaf blower. I fed the bag down through the vent, and then turned the leaf blower on. I don't believe this pushed much more out, but it did assure me that the blockage was gone because the air flowed through.