If a sewer main backs up, which part of the system is likely to fill first?

If a sewer main backs up, which part of the system is likely to fill first?

• A. Service lines will fill up
• B. House service lines will fill up
• C. Main sewer will fill up
• D. Lateral connections will fill up

Answer: (A)

When a sewer main backs up, the first place backflow reaches is the lines that are directly connected to that main. The service lines are the closest branches to the main, so as pressure builds from the blocked downstream point, wastewater will begin to enter these service lines first. The house service line (the portion inside the property) and the other lateral connections are farther along the path and typically won’t fill until the backflow progresses further or pressure increases more. This is also why we install backwater valves on service lines or at the building to prevent sewage from backing up into homes.

When a sewer main backs up, the first place backflow reaches is the lines that are directly connected to that main. The service lines are the closest branches to the main, so as pressure builds from the blocked downstream point, wastewater will begin to enter these service lines first. The house service line (the portion inside the property) and the other lateral connections are farther along the path and typically won’t fill until the backflow progresses further or pressure increases more. This is also why we install backwater valves on service lines or at the building to prevent sewage from backing up into homes.