Signs, Causes & Troubleshooting a Clogged Sewer Line

Image: Sonoma City

A clogged sewer line is a plumbing issue that can lead to serious problems if not addressed promptly. Here’s a brief summary of the signs, causes, and troubleshooting steps for a clogged sewer line:

Signs of a Clogged Sewer Line

  • Slow Drains: Multiple drains in your home, such as sinks, tubs, and toilets, are slow to empty or gurgle when in use.
  • Backups: Frequent backups in toilets, sinks, or bathtubs, often with sewage coming up from one fixture when another is used.
  • Foul Odors: Persistent foul sewage odors in or around your home, especially in the yard or basement.
  • Water Level Changes: Unexplained changes in the water level in your toilet bowl or floor drains.
  • Gurgling Sounds: Gurgling or bubbling sounds coming from drains when using plumbing fixtures.

Causes of a Clogged Sewer Line

  • Tree Roots: Invasive tree roots can infiltrate sewer pipes, causing clogs and damage.
  • Grease Buildup: Accumulated grease and fats can constrict sewer pipes over time.
  • Foreign Objects: Flushing non-flushable items like wipes, paper towels, or sanitary products can lead to clogs.
  • Aging Pipes: Older sewer pipes can deteriorate, corrode, or collapse, causing blockages.

Troubleshooting a Clogged Sewer Line

  • Professional Inspection: If you suspect a clogged sewer line, contact a professional plumber or sewer specialist for an inspection.
  • Video Inspection: Plumbers often use video cameras to inspect the sewer line’s interior, identifying the location and cause of the blockage.
  • Snaking or Augering: Plumbers can use drain snakes or augers to break up clogs and clear the sewer line.
  • Hydrojetting: High-pressure water jetting can be used to remove stubborn blockages and clean the interior of sewer pipes.
  • Pipe Replacement: In severe cases of pipe damage, sections of the sewer line may need replacement.
  • Preventative Measures: To avoid future clogs, follow proper disposal practices, avoid planting trees near sewer lines, and schedule regular sewer line maintenance.

It costs between $100 and $500 to unclog a sewer line. A plumber will charge you more if they have to run a sewer camera prior, which they almost always do. The cost will be more if you don’t have a sewer clean out and they have to remove a toilet to access the sewer line.

To unclog a sewer line without a sewer cleanout, you will need to remove a fixture like a toilet to access the sewer line. Alternatively, you can do it from the roof via the plumbing vet. Both of these methods have a low success rate compared to a sewer cleanout.

How a Sewer Line is Designed

Image: NextDay Inspect

As I mentioned earlier, a sewer line is the horizontal line running underground in your yard connected to the public sewer line or septic tank. On the other end, it is connected to the house’s main drain stack which is a vertical pipe.

In case you are wondering, the sewer line between your house and the street is the homeowner’s responsibility, which also includes the sewer cleanout. This means that each homeowner is responsible for repairs and maintenance costs of their sewer line.

The city is responsible for sewer lines only when the problem is in the public sewer lines along the street. The section between the street and the house is the responsibility of the homeowner.

The main drain stack is also connected (above the highest fixture) to a vertical pipe called a plumbing vent which runs through the roof of the house.

The plumbing vent is responsible for expelling sewer gases/odors out of the system and also introduces air into the drains. This is what allows fixtures to drain faster.

Each of the fixtures has their own drainpipe (branch drains) which drains into the main drain stack. As a result, a plumbing diagram looks like a tree, with the truck representing the drain stack while the branches represent each of the fixture’s drainpipes.

This means that if is there is a clog somewhere in the sewer line; it will affect all the fixtures in your houses. Fixtures on the low levels of your house will be the first to be affected.

Signs of a Clogged Sewer Line

So, how do you know that you indeed have a clog in your main sewer line and that you are not dealing with just one clogged fixture? And how do you know that the clog is in your sewer line and not the main drain stack in your house?

The following are the telltale signs of a clogged sewer line:

1. Slow Draining Fixtures

There are 2 types of clogs; full and partial clogs. Full clogs are those that will not allow wastewater to flow past them while partial clogs will only allow waste to flow out slowly.

Most clogs start off as partial clogs before developing into full clogs. With a partial clog, you will note that your fixtures (bathtubs, washing machines, sinks) are draining slower than they should.

As I had mentioned earlier, slow draining fixtures can also be caused by a clogged plumbing vent. Just to be sure that the problem is with your sewer line and not vent stack, climb to the roof of your house armed with a garden hose.

Stick the garden house inside the vent and check if there is any blockage. If you do not want to stick the garden hose inside the vent, a drain auger is a good alternative.

2. Backing Up Basement Floor Drain

Being the lowest point (or drain) in your house, your basement floor drain will be first to start backing up in case of a clogged sewer line. This drain is installed low to remove any water in the basement floor to prevent flooding.

If you notice sewage backing up from your basement floor drain, it is a clear sign that the sewer line is clogged. Turn off electricity around that area and avoid using any water fixture. Call a plumber immediately.

3. Gurgling and Smelly Drains

If your toilet gurgles or bubbles when flushed, you either have a clogged sewer line, main drainpipe or plumbing vent. That is also the case when the tub/shower drains gurgles when you flush the toilet.

You may also notice the toilet, shower/tub or sink drain backs up or gurgles when the washing machine is draining. Why is this case?

As wastewater accumulates inside the drainpipe, air starts to build up above it. That is not a problem however since your house has a vent.

The problem starts when the wastewater column rises passed the branch drainpipes. This causes waste and air bubbles to accumulate inside the branch drainpipes.

Since the gases/air cannot flow out through the vent, they are forced to come out through the fixture drains. As you might know, every drain has U-bend called a P-trap full of water. Just like the one at the bottom of your toilet bowl.


As the gases are forced out passed the water, it causes it to bubble and hence the bubbling toilet as the tub/sink drains.

Flushing the toilet or draining the washing machine will also create a vacuum (since the vent is now inactive). The vacuum sucks the water from the tub’s P-trap and hence the gurgling sound.

Air escaping from the drains is what causes the sewage smell in your house. If the problem is not fixed and you continue using the fixtures, raw sewage will soon start to back up from the drains.

Causes of a Clogged Sewer Line

Clogged Sewer Lines are caused by one or a combination of the following factors:

1. Tree Roots

Unlike today when sewer lines are made of PVC, old sewer lines were made of porous materials like clay. If you have trees close to the sewer line, it is natural for the roots to grow towards the water and nutrients found in the sewage.

Tree roots can also grow through tiny cracks or loosely connected cast iron sewer pipes. Although this tree roots are initially very thin and incapable of clogging the sewer line, the nourishment from the sewage helps them to rapidly grow in size inside the line.

After a few years, wastewater will be completely blocked resulting in backing up drains.

2. Sagging Pipes

Sagging pipes refers to a condition where a section of the sewer line becomes bellied (or curved inwards) due to soil movements. As I had mentioned, the sewer line is supposed to slope from the house to the street.

When the sewer line starts to sag, it inhibits movement of waste, which will over a period of time get trapped in the belly of the pipe causing a clog.

3. Flushing what You Shouldn’t

Flushing wet wipes, too much toilet paper, contraceptives, sanitary products, dental floss, diapers and other things that you shouldn’t flush is the fastest way to clog your drainpipe or sewer line.

These things accumulate inside the sewer line over a period of time and later form a ball that completely blocks it.

The only thing that you should actually flush down your toilet is toilet paper and human waste. Any other thing is likely to clog the drainpipe or sewer line.

4. Pouring Grease Down the Drain

Never think of pouring grease after cooking French fries or bacon down the sink drain. I know some people say it is okay to do so as long as you run hot water and soap but it isn’t.

The cooking oil will afterwards separate from the water, cool and solidify resulting in clogs in your sewer line. It also combines with other compounds in water like calcium to form a sticky waxy substance which will cause a severe clog.

What you should do after cooking is pour the oil in a sealable container and then put it in the trash. See what to do if you accidently pour grease in your drains in this post.

How Do I Unclog My Main Sewer Line?

As I had mentioned earlier unclogging the main sewer line should be left to professionals. There are so many things that can go wrong if you decide to do it yourself.

To start with plumbers have the experience and the right tools to deal with the problem. For instance, they will start by running a sewer camera to know what type of clog it is, and what blade to attach to the drain auger.

What you can do is to first try and locate your sewer cleanout so that a plumber will have an easy time once they arrive.


Usually, a sewer cleanout will be found outside but very close to the house sticking a few inches from the ground. It has a cap with a square nut at the top.

If you are quite handy and want to fix the problem on your own, grab a wrench and slowly start to loosen the sewer clean out cap.

It is not a good idea to remove the cleanout cap if you already have sewage backing up from your drains. It means the vertical drain stack is full of raw sewage and the moment you remove the cap your yard (and yourself most likely) will be covered in raw sewage.

If you manage to remove the cleanout cap, insert a drain auger/snake and try to break the clog. Call a plumber if the clog won’t budge.

How to Unclog Main Sewer Line without a Cleanout

So, what happens if you have to unclog a main sewer line but you have no sewer cleanout anywhere on your property? There are 2 things you can do.

The first thing is to climb to the roof of the house and access the sewer line from the plumbing vent. Secondly, you can remove a fixture like a toilet and feed your snake through its drainpipe.

Both of the above methods are less than ideal but sometimes they are the only option you have. Plumbers will do the same, though they will charge more as it involves more work.

The only problem is that if a plumber snakes the sewer line through the vent or toilet drain, they will not give a warranty for their job. Warranty is only given when the line is snaked through the cleanout.

Wrap Up

To be on the safe side, it is important to make sure that your main sewer line is cleaned frequently. Once a year would be ideal.

If you do not have a sewer cleanout already, consider installing one. However, if your sewer line is made of cast iron and you do not have a cleanout, you can wait until when you need to replace the whole sewer line.

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