Figure 1-3. P-trap for sanitary plumbing fixture.
Main sewer. A sewer line to which two or more branches are
(6) Trunk sewer. A sewer with many branches which provides the outlet for
a large geographic area.
(7) Force main. A sewer main carrying wastewater under pressure from a
(8) Inverted siphon (depressed sewer). A portion of a sewer line that is
placed deliberately below the drainage grade of the rest of the line such that the
depressed portion is filled with wastewater at all times. It is especially useful for filling
pumps at a pumping station.
(9) Manhole. A manhole is used to enter the sewer system to inspect and
to clean the line. Whenever the sewer pipe changes direction, a manhole is required,
300 to 400 feet apart. For large mains of 60 inches, manholes are often spaced from
300 to 600 feet apart.
Pumping station. A place for pumps and other equipment which lifts
wastewater to a higher elevation.
Outfall sewer. A sewer line leading from a collecting system (or from a
treatment plant) to the final disposal point.