Main Sewer Line Problems: Warning Signs, Costs, and What Homeowners Should Know

Created by AI

Walking the dog today, I found one of the blocks in my neighborhood closed. They were replacing the mainline sewer. A mainline sewer is the large, primary underground pipe that collects wastewater from all the drains in your home (sinks, toilets, showers, and appliances) and carries it away to the municipal sewer system or a septic tank, acting as the central "highway" for your entire home's drainage. It connects to smaller drain lines, and if it clogs, it can cause sewage backups and drainage issues throughout your house. 

Since we live in an older neighborhood, we have many old trees, 50+ years. These trees have deep roots, and our homes often have clay sewer pipes. The roots grow into the sewer pipes and eventually cause problems. Many of our neighbors have had their mainline sewer pipe replaced recently. Before you have an emergency with a sewer back-up, which will most likely cost you more, I have some information about what you need to know:

How To Know When It’s Time to Replace Your Mainline Sewer Pipe

Main sewer line clog symptoms include multiple slow drains, gurgling sounds from toilets or drains, foul sewage odors, water backing up in the tub or shower when flushing, and wastewater pooling in your yard or overflowing from the sewer cleanout. Together, this indicates that you need a new mainline sewer pipe. 

• Slow & Multiple Drains: All drains (sinks, tubs, showers) drain more slowly than usual, or you have frequent clogs in various spots

• Gurgling Sounds: You hear bubbling or gurgling from toilets or drains, especially the toilet, when using other water fixtures

• Water Backups: Water comes up in your tub or shower when you flush the toilet, or raw sewage appears in low-level drains like basement floor drains

• Sewage Odors: Strong, unpleasant smells of sewage coming from drains or fixtures. 

• Yard Issues: Lush patches of grass or actual sewage pooling in your yard, often near the sewer line

• Sewer Cleanout Overflow: Water or sewage backs up and comes out of the exterior sewer cleanout pipe

• Foundation problems: Foundation cracks caused by soil saturation from leaks

What Causes Mainline Backups?

• Roots growing into the cracks of your mainline sewer pipe

• Heavy grease build-up

• Sediment

• Non-flushable items like wipes (baby, cleaning, facial), feminine hygiene products, paper towels, dental floss, cotton balls/swabs, hair, and diapers

Ideas to Consider Before Replacing Your Sewer Line

Before replacing your sewer line, you might have your line ‘snaked’ by a professional sewer company to see if that helps eliminate clogged lines. Because we have several old trees in our yard, we have our lines snaked once a year to make sure they’re functioning correctly. 

What is ‘snaking’? Snaking a main sewer line involves feeding a motorized, flexible cable (auger) into the main cleanout (usually outside the house) to break up or pull out deep clogs like grease, wipes, or tree roots, requiring safety gear (gloves, glasses) and care to avoid pipe damage or injury. 

It is possible to snake it yourself if you have clogs within the first 50-100 feet, if you're comfortable with tools and have a motorized auger from a home center. But it’s often recommended to hire a professional. Why? To prevent worsening issues or pinpoint root intrusion with a camera.

A professional, though, will have a camera to see where the blockage is. They will also have the correct equipment to remove the blockages and restore flow. Snaking a sewer line with a professional usually costs about $100 to $250. 

What If Your Mainline Must Be Replaced?

If a mainline sewer has to be replaced, it’s often due to old age, tree root intrusion, ground shifting, or improper installation. A crumbling mainline pipe will cause problems such as frequent clogs, sewage back-ups, foundation problems, and foul odors. Replacing your mainline sewer pipe will eliminate problems since it will be a new pipe and up to code. 

Common Reasons for Replacement:

• Age & Material: Older pipes, especially clay or cast iron, corrode, crack, and crumble over time, often outliving their usefulness

• Tree Roots: Roots seek water and grow into pipe cracks, causing blockages, breaks, and collapses

• Ground Movement: Soil shifts and settling can misalign, crack, or break pipes

• Corrosion: Rust and corrosion weaken metal pipes, causing leaks and failures

• Poor Installation: A flawed initial installation can lead to ongoing problems that only replacement can fix

• Extensive Damage: Multiple cracks, significant deterioration, or a collapsed pipe often make replacement the only viable option

What to Expect from a Mainline Replacement

• Replacing a main sewer line typically costs $3,000 to $10,000, but can range from $1,000 to over $20,000, depending on the method (trenchless vs. traditional digging), pipe length (often $50-$250 per foot), obstacles (driveways, roads), soil conditions, and local labor/permits, with trenchless often cheaper for landscaping but excavation potentially less upfront but costly for restoration. 

Cost by Method & Length

• Traditional Excavation: Digging up the line; can be cheaper initially, but expensive for yard restoration.

• Trenchless (Pipe Bursting/Lining): Less disruptive but often higher upfront cost; ideal for avoiding landscaping damage.

• By Length: Costs often rise with length; a 25-35 ft section might start at $1,250+, while longer runs (75-100 ft) can hit $3,750 - $20,000+. 

Key Cost Factors in Denver

• Depth: Denver's deep frost line means deeper burial, increasing costs.

• Obstacles: Roadways, driveways, concrete, or large landscaping add significant expense (potentially thousands).

• Pipe Material: PVC is cheaper than copper or cast iron.

• Permits & Inspections: Required city fees add to the total. 

How to Get an Estimate

• Camera Inspection: Essential to pinpoint damage and get an accurate quote.

• Multiple Quotes: Get written bids from 2-3 companies to compare scope, not just price. 

  
  

What to Watch For

• Hidden Costs: Ensure quotes include demo, road cutting, and full restoration, as these vary widely.

• Local Expertise: Choose plumbers familiar with Denver's specific regulations and soil.

  
  

Prevent a Sewer Emergency Before It Starts

Mainline sewer problems rarely appear overnight—they give warning signs long before a costly backup occurs. Slow drains, gurgling toilets, sewage odors, or soggy patches in your yard are signals that shouldn’t be ignored, especially in older neighborhoods with clay pipes and mature trees.

Annual sewer line cleaning and periodic camera inspections can catch issues early, saving you thousands in emergency repairs and property damage. If replacement becomes unavoidable, working with an experienced, local sewer professional ensures the job is done correctly, up to code, and with no hidden surprises.