How to clean dryer ducts . Home is built on a slab
It's very important to clean your dryer air duct at least annually.  Accumulated dust in them is a common source of house fires.  Usually they come apart in sections.  Typically what you do is remove the sections and vacuum or brush out the dust.  They also make telescoping dusters that have a round duct-sized brush on a flexible wire that you can use to push the dust through.