This is a picture of a two inch kitchen sink trap that is in most home's , If this client would have had regular service on there drain lines they would have avoided a costly reapair.  

And the damage did not stop at the kitchen sink where it was all exsposed it went in the walls where you can't see the damage starting , This client figured they could fix that slow drain with a chemical drain opener sold to them at a local home center but the home center man did not tell them that the drain opener can cause corosion of there pipes in there home and not to mention a list of other things that could happen usiing chemicals in your home.