Progress,  page 19
Here is a closeup of the vent loop for the kitchen sink drain.  The sink will be in an island in the
middle of the kitchen, so it is not possible to run a normal vent line up trhough the ceiling.  In
such cases, the vent line is returned to the drain line a short distance downstream from where
the sink water enters.  Normally 2 inch drain line is used for sink drainage, but we fed the 2 inch
vertical portions into a 3 inch diameter drain line to assure that there would be unrestricted
venting from the drain.  It wasn't really necessary, but it was cheap insurance.
To make sure that sharp rocks didn't damage the ABS drain lines as we finished backfilling and
compacting, or during later settling, we hand packed sand under and to the side of the lines and
then covered the rest of the lines with a few inches of pea gravel.  Here you can see both.

As I write this, both the black water and gray water lines for the kitchen, dining room, and
laundry room have been trenched, installed, and covered.