A lateral sewer is a sewer which connects a structure to the main sewer line. Technically, a later sewer is not supposed to have any tributaries, but on a multifamily property, the lateral sewer may actually split to reach the plumbing of several different residences. The lateral sewer connects the indoor plumbing of a house with the sewer lines which carry waste away for treatment and processing.
Technically, the lateral sewer is the responsibility of the property owner. When someone constructs a new building, they must pay for connection to the sewer system, including placement of a lateral and the placement of meters to monitor usage. Monthly fees must also be paid, usually on the basis of how much water is routed into a structure, with the logic that what comes in must come out. However, once installed, the responsibility can become nebulous.
The issue is that while a lateral sewer belongs to the property, if a problem develops, it can become a public health issue. This means that sometimes officials may step in to address a problem, even though it is not their legal responsibility, in the interests of keeping people safe. In many communities, programs which pay for inspections of laterals and which will defray the costs of repairs are available. These programs ensure that issues such as breaks and blockages are addressed before they become a problem.
The most common problem which arises in the lateral is a blockage. Blockages are addressed by accessing the sewer clean out, a pipe which juts out of the lateral, usually just before it enters the structure. A snake and other devices can be put into the cleanout to clear the blockage and allow wastewater to run freely down the lateral. Leaks and breaks are another problem, especially in areas with cold weather, or when a lateral is broken by construction, digging for utility placement, and so forth.
The sewer lateral is generally designed to run downhill, so that gravity pulls the contents into the sewer main. This helps to reduce the risk of backflow, an undesirable situation in which raw sewage bubbles back up into household plumbing such as the shower. However, a blockage can force wastewater into the household plumbing because it has nowhere to go. When backflow occurs, it is important to bleach the area after the blockage has been cleared, as raw sewage can contain harmful microorganisms.