Rather than cleaning this dangerous flexible venting we installed rigid pipe through the floor of the laundry room and out the wall. This was a short run but fairly tricky transition to the outside wall. It came out very nice and allows for much better airflow and maintenance.
No more flex!
We removed this dangerous flexible vent and replaced with rigid duct work.
New rigid vent
Our new vent properly secured with metal strapping and taped with mastic. The homeowner reports his clothes have never dried faster!