Before the backfill process, many drainpipes are installed. These include drainpipes around the perimeter of the foundation wall, drain pipes throughout the interior of the foundation, drain pipes to daylight, drain pipes for the bathroom, laundry and kitchen fixtures. Of course, the plumbing drainpipes are all pressure tested for leaks.
In Patient Chickadee, the concrete floor of the first floor will be the finished floor so all drainpipes go in first. No one wants to jack hammer through concrete to fix a drainpipe!