Kevin Cook for Idaho Senate Ribbon

Whether you are a homeowner or a property manager, understanding the plumbing systems in your building is key to keeping them operating efficiently. One of the most important components of your plumbing system is the main sewer line. A main sewer line is a vital piece of infrastructure that is responsible for transporting waste and wastewater from your building to the municipal sewage system. In this beginner’s guide, we’ll take a deeper dive into what a main sewer line is and how it functions.

What is a Main Sewer Line?

A main sewer line is a large-diameter pipe that connects your building’s plumbing system to the municipal sewage system. It is responsible for carrying wastewater and sewage away from your building and into your city’s treatment plant. The main sewer line is typically located underground and runs from your building’s plumbing system to the sewer located in the street. The size of the main sewer line can vary depending on factors such as the size of the building and the type of plumbing system.

How Does a Main Sewer Line Work?

The main sewer line relies on gravity to transport wastewater and sewage away from your building and into the municipal sewer system. When water is used in your building, such as when you flush a toilet, it flows down the main sewer line and into the city’s sewage system. The main sewer line is designed to maintain a minimum slope so that gravity can continually pull waste and wastewater away from your building.

What Are Common Problems with Main Sewer Lines?

Over time, main sewer lines can become clogged with debris such as grease, food particles, and hair. This can lead to slow draining sinks, toilets, and showers. Additionally, tree roots can grow into the main sewer line, causing blockages and damage to the pipe. If left untreated, clogs in a main sewer line can result in sewage backing up into your building, leading to foul odors and potentially hazardous bacteria.

How Can You Maintain Your Main Sewer Line?

One of the best ways to maintain your main sewer line is to avoid flushing anything down the toilet other than human waste and toilet paper. Items such as baby wipes, feminine hygiene products, and even wet wipes should be thrown in the trash. Additionally, you should avoid pouring grease or cooking oil down your drain and be cautious about what you put in your garbage disposal.

Another important step in maintaining your main sewer line is to schedule regular annual inspections and cleanings with a professional plumbing company. Professional plumbers will use specialized equipment to remove any blockages or debris from your main sewer line.


Understanding what a main sewer line is and the importance of keeping it maintained is critical to the health and safety of your building’s occupants. A well-functioning main sewer line ensures that wastewater is disposed of correctly and minimizes the likelihood of potentially harmful sewage backups. By following a few easy maintenance tips and scheduling regular inspections with a professional plumbing company like S3 Plumbing, you can keep your main sewer line operating smoothly for years to come.