Franchise Opportunities
Call Now 1-866-758-6237

Drain Cleaning | March 19, 2026

What Causes A Belly In Sewer Line? (And How To Fix It!)

What Causes A Belly In Sewer Line? (And How To Fix It!)

A belly in your sewer line is a problem that needs to be fixed immediately. Let’s take a look at what it is, why it’s a problem, and how to repair it.

What is a Belly in Sewer Line?

A sag in your sewer pipe is also known as a belly. Unfortunately, the pipe continues to hold water in the belly after the flow of water has stopped. The belly creates a negative slope which pools water and waste inside the pipe.

Sewer line bellies can become a huge issue because they collect debris and begin causing backups in the sewer line. That backup of waste water will find itself on your property and in your home if it’s not taken care of. And that leads to thousands of dollars in damage from wastewater flooding.

diagram of belly in sewer line
A sewer line needs to slope downward and the correct angle (or pitch), away from the home. When a belly (or sag) occurs, it changes the slope and allows wastewater and other debris to collect. Eventually, this creates a backup and possibly flooding back into the home.

Why Your Sewer Line is Bellied

More often than not, a belly in the sewer line is caused by geological events. These include soil erosion, foundation settlement, or earthquakes. It can also occur from human error like poor installation or poor soil compaction. 

Keep in mind that a belly usually happens at the fitting of the pipe (where two pipes connect). A pipe bending outside of the fitting is unlikely, especially for cast iron, because this would require extreme pressure for it to bend.

belly in sewer line causes blockage diagram

This image illustrates how the belly dip in the pipe collects waste which eventually blocks the pipe. Notice how this occurs at the joint (fitting) where two pipes come together.

How to Fix a Belly in Sewer Line

A sewer camera inspection will reveal if the sewer line is bellied. Unfortunately, the only way to really fix it is to have it dug up and replaced. In other words, it requires excavation and replacement.

Excavation is the only effective way to get at the problem and correct the slope of the pipe. If this isn’t done, the pipe will continue to cause larger issues as it collects more water and debris in the belly. 

excavation of belly in sewer line

Sewer repair excavations are usually bigger jobs that require the proper equipment and a sewer excavation crew of 2 or 3 people. Understanding the process will benefit you and your property. 

What is Sewer Line Channeling?

A drain specialist or experienced plumber who looks at your sewer line belly will also look for a similar problem called sewer line channeling.

Sewer line channeling happens when running water cuts a course into the bottom of the sewer line (similar to a ravine, canyon, or gully). Often, by the time this problem is discovered, the bottom area of the pipe is partially or completely gone. 

When the sewer line bottom is completely gone, tree roots take over the pipes, and insects have an easy way into your home. 

sewer line in belly vs sewer line channeling

As you can see in this diagram, a belly in sewer line is different than sewer line channeling. The belly has not actually caused the pipe to break or erode away (yet!). Channeling is when the water has carve out a path that will eventually break or erode the pipe.

How Do I Fix Sewer Line Channeling?

There is a way to fix sewer line channeling and it is called trenchless pipelining.

Trenchless pipelining is less destructive to your property because it does require an excavation crew. Although it can be more expensive, it is an environmentally friendly way to fix a damaged pipe caused by channeling.

diagram of trenchless pipelining to repair sewer line channeling

An epoxy-saturated felt liner is inserted into the pipe and then cured in place. The result is a new PVC-quality pipe inside the old one. Life expectancy is up to 50 years.

Final Thoughts 

What causes a bellied sewer line can help you understand why you might be experiencing backups or blockages. But fixing it is difficult and expensive, though cost depends on how deep and pervasive the problem is.

Sewer line channeling can also cause major problems with your sewer line if it is not addressed. For this problem, pipelining might be the right solution for you as it causes less damage to your property.

Call 1-Tom-Plumber

Don’t hesitate to contact us here or call us at 1-Tom-Plumber (1-866-758-6237) if you suspect a belly, or are experiencing backups from your sewer line.

1-Tom-Plumber’s certified team of plumbers and drain technicians respond immediately to any emergency plumbing,drain cleaning, or water damage problem. We also handle the excavation of underground water lines and sewer main lines. Our immediate-response team is available every day and night of the year, even on holidays.

Related Blogs