Hello:

My daughter is purchasing a house in which the washing machine drain is tapped directly into a 4" clean out plug in the vertical cast iron main line. I realize this is not to code, and gas could back up into the washing machine. However the house inspector said that since the water was going straight into the 4" drain pipe, and hitting the opposite side of the pipe that it would wear a hole in the cast iron pipe. This seems a little extreme to me, but can the pressure created by a washer pump wear a hole in cast iron? Thanks for any advice.
Michael.

You need a new home inspector. This drain is certainly not code and it will be a problem. Tell the seller it must be fixed or you will lower your offer enough to have it fixed. Water and/or sewer gas will back into the washer.