Pay special attention to the joints so roots do not grow into the piping. The depth of the piping should be below the frost line. Also, you should encase the piping with concrete or sleeve it with a metallic material when laying piping under roadways.
It may be necessary to install the building sewer and the water-service pipe in the same trench (fig. 7-1). If so, use the following precautions:
Figure 7-1. - Building sewer and the water-service pipe in the same trench.
Ensure the bottom of the water pipe is at least 12 inches above the top of the building sewer.
Place the water pipe on a solid shelf at the side of the trench.
Use hot lead when joining cast-iron pipe for a building sewer; use a hot-poured compound in joining bell-and-spigot clay or concrete sewer pipe.
After installation, test the building sewer with a 10-foot head of water, or equivalent test.
Install sanitary drainage piping on a uniform slope. This slope, pitch, grade, or drop per foot decides the flow velocity of liquid within the pipe. Piping with a diameter of 3 inches or less requires a slope of not less than 1/4 inch per foot. Pipe 4 inches or larger slopes no less than 1/8 inch per foot. This allows a velocity of not less than 2 feet per second, that provides the scouring action necessary to keep a pipe free from fouling. Sewer mains may have slopes of less than 1/8 inch per foot, as long as there is a cleaning velocity of 2 feet per second or greater. See table 7-1 (A) for code requirements.
Table 7-1 (A). - Discharge Rates and Velocities of Sloping Drains