Sewer Line Terms You Should Know


When it comes to sewer lines, there are many technical terms that can be confusing for homeowners. Understanding these terms can help you make informed decisions about repairs and maintenance. In this post, we’ll cover some of the most important sewer line terms you should know, including the main line, service line, tap, clay line, off-set, collapsed line, belly, sewer scope, clean-out, and pipe bursting. By the end of this post, you’ll have a better understanding of these terms and how they relate to your home’s sewer system.

What is the main line?

The main line is the city’s responsibility and connects your service line to the city sewage treatment center. It is typically 10 inches in diameter and runs under your street or alley.

What is a service line?

Your service line is typically 4 inches in diameter and runs from your house to the main city line. The homeowner is responsible to repair the service line- even if it is in the street or alley. 

What is a tap?

A tap is the connection between your service line and the main city line, which is typically located in the public right-of-way (alley or street).

What is a clay line or clay tile?

Before 1975, sewer lines were made of clay pipe, which are susceptible to tree-root infiltration and have multiple joints that can become separated or misaligned, causing leaks. Ground settling and erosion also can cause older pipes to move or collapse. Many Denver Metro homes still have the original clay pipes. Current plumbing code requires schedule 40 PVC or SDR 35 be used.

What is an off-set?

An off-set occurs typically in a clay line. Clay lines are in 3-5 foot sections and there are joints every 3-5 feet when the sections come together. If those joints move out of place so they are not in line there will be an off-set. Depending on how severe the off-set is, you may or may not notice a difference in the function of your line.

What is a collapsed line?

A line can be fully or partially collapsed. You will most likely notice disruption in your plumbing service. Having a back-up is generally the first indicator that you have a collapsed line.

What is a belly?

A belly is a low spot in the line where water and/or sewage collects. This may or may not disrupt service. Often times, a belly is discovered only when a sewer scope is done on a sewer line.

What is a sewer scope?

A sewer scope is when you use a special camera to visually inspect the interior length of the line. This will aid in locating blockages, bellies, obstructions, etc. This also helps us located exactly where the line needs to be repaired. The camera generally enters the line via a vent stack on your roof, a toilet or a clean-out.

What is a clean-out?

A clean-out is an access point, typically put in your yard next to the house. They are used to easily access your sewer line in order to inspect or clean it out. When a sewer line is replaced, we generally add two clean-out locations. This will make it easy down the road to maintain your sewer line.

What is pipe bursting?

Pipe bursting is a process of replacing an existing line by pulling a new line through the existing line. This may or may not be an option depending on the condition of your current line and restrictions in certain municipalities.


In conclusion, understanding sewer line terms is important for homeowners to know their responsibilities and potential issues. Knowing the difference between the main line and service line, and common issues like off-sets, collapsed lines, and bellies, can help homeowners prevent major problems and make informed decisions about repairs. A sewer scope and clean-out are also valuable tools for maintaining and repairing sewer lines.