The fifth major step in building a home is installing the underground plumbing. The plumbers start at the sewer lateral that comes under the footing from the street and slope it upwards to all the areas that plumbing is necessary like the utility room, bathrooms, kitchen, etc. It is common to only put in the drains under ground and after the home is framed the water supply lines will be installed. After all the drains are installed the plumber will either put water in the pipes or put a pressure gauge on the top of one of the drains. All the other line ends will be capped and then after a little time the water or gauge will be checked to make sure there is no loss. This ensures that there are no leaks in the lines.
The plumbing lines must be covered with sand or small gravel. No large stones that could puncture the pipes are allowed.
The above picture is the underground plumbing for a bathroom. The black box is on top of the bath tub drain, it keeps the concrete from being around the drain so the plumber can easily get to it later. The large pipe is the toilet drain and the small pipe with the pressure gauge on it is for the sink drain.