Here's a piece of a 60-year-old 1.5" steel drain pipe that was removed from our house. The hole in the middle was a bit smaller before the person who removed it poked his little finger in it. The drain handled both the kitchen sink (with dishwasher) and laundry tub (with washing machine). We bought the house 9 years ago and had to have the drain snaked out twice, so we decided to replace the pipes with 1.5" ABS. Hopefully we'll never have to call a plumber for it again!