The plumber, a firefighter by trade, came out and installed a sewer drain.  The #9 PVC pipe is the drain cleanout, and the #4 will be the main sewer line to the fixtures in the house. I didn’t locate the drain clean out on the drawings, so the plumber picked a location he knew would be accessible by a truck if it were ever necessary to clean out the drain with a pump.  Unfortunately, this spot is directly in the middle of my future yard.  Next time I will indicate that the  drain clean out should be in the sidewalk.  The plan, for now, is to cut the drain clean out below grade and let grass grow over it.  We will mark the spot with some indicator, or perhaps a metal rod that can be identified with a metal detector.