A 3rd floor condo with 6 units above and 2 below. There have been 5 kitchen sink backups in the past 44 months. 3 out and over the top with gray water. No one is home and the dishwasher is not on. The Lead Plumbing Inspector after looking at a video of the inside said the 3" vertical drain pipe bends slightly on it's way to the 2nd floor and and the cast iron is pitted. Building built in 1989 and converted to condos in 2005.