Most developed areas dispose of waste through the same methods the Romans used more than a thousand years ago. The idea is to remove waste from a higher location to a place at a lower location through a pipe, with the force of gravity doing the actual removal. This is why they are referred to as “gravity sewer” lines. Gravity sewer will travel from individual homes to the wastewater treatment plant. At the home, a sewer line will be either 4” or 6” in diameter and increase in size to a few feet in diameter, each increase being required by a larger amount of “flow” or sewage.
Sewer pipe material has varied over time. The romans used stone. Over the past century, materials have included cast iron, brick, terra cotta, green-burg, and asbestos. Modern sewer systems consist primarily of ductile iron, PVC, and HDPE.
Maintenance becomes an issue after hundreds of years of sewer service. Pipes must be inspected, replaced, and maintained in order to keep things flowing smoothly. On a private property, “cleanouts” or sight-inspection ports are used to provide access, yet only on a very limited scale. These methods only provide a 4”-6” access to the sewer line, enough for a sewer machine, CCTV probe, or jetter. For larger commercial sewer lines or sewer lines belonging to a municipality, maintenance access is provided by manholes, usually spaced every 300’-400’ apart. A manhole is a shored hole of at least 48” in diameter which allows for a person to lower him or herself down to the pipe elevation. The bottom of the manhole contains troughs or “inverts” which guide the sewage flow through the manhole unimpeded. Manholes are made of stone, brick , or concrete.