Sewage Backing Up in Basement? Why and What to Do

Sewage backing up in the basement is usually caused by a clogged sewer line. Since waste cannot flow out of the house, it starts to back up through the basement since it is the lowest level in the house.

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Sewage Backing Up in Basement: Causes and What to Do


  • Blockages: Sewage backups in the basement can result from blockages or clogs in the main sewer line or the drain lines leading from your house. These blockages can be caused by debris, grease buildup, tree roots, or foreign objects.
  • Tree Root Intrusion: Tree roots seeking moisture can infiltrate sewer pipes, causing cracks and blockages that lead to sewage backups.
  • Pipe Damage: Aging or damaged sewer pipes can develop cracks, fractures, or collapses, allowing sewage to escape into the surrounding soil or back into your basement.
  • Heavy Rainfall: Intense rain can overwhelm the municipal sewer system, causing it to back up and push sewage into your basement through floor drains or toilets.

What to Do

  • Safety First: Ensure the safety of occupants by evacuating the basement if necessary and avoiding contact with sewage-contaminated water.
  • Shut Off Utilities: Turn off electricity to the basement to prevent electrical hazards, especially if water is present.
  • Call Professionals: Contact a licensed plumber or sewage cleanup service to assess the situation and address the underlying causes of the backup.
  • Locate the Blockage: If it’s a localized issue, such as a blocked drain line, a professional can use a camera inspection to identify the problem’s exact location.
  • Clear Blockages: Professional plumbers can use high-pressure water jetting or augers to clear blockages or remove tree roots from sewer lines.
  • Repair or Replace Pipes: Depending on the extent of damage, pipes may need repair or replacement. Trenchless methods, like pipe lining or bursting, can minimize excavation and disruption.
  • Cleanup and Disinfection: After resolving the issue, thoroughly clean and disinfect the affected area to prevent health risks associated with sewage contamination.
  • Preventive Measures: Take steps to prevent future sewage backups, such as installing backwater valves or regular maintenance of your plumbing system.
  • Contact Insurance: If you have sewage backup coverage in your homeowner’s insurance policy, notify your insurance company to start the claims process.
  • Local Regulations: Be aware of local regulations and permits related to sewage backups, as some municipalities may have specific requirements for cleanup and prevention measures.

How Your Sewer Line Works

You house has several drains (toilets, sinks, showers, tubs, washing machines) each with a separate drain line. This is why you could have a clogged toilet while the bathroom sink is draining normally.

Each of the drain lines are then connected to the main house drain stack. This is a vertical drainpipe of about 4 inches in diameter and it is also where the drains in the basement are connected to.

The main drain stack is then connected to the sewer line. This is a horizontal line that carries sewage away from your house to the city’s sewer line near the street or septic tank.

Sewer lines are installed sloping towards the street or septic tank so that waste can flow out via gravity.

If the main drain stack is clogged, the drains in the higher levels of the house would be the affected and, and you would notice sewage backing up from the toilets and shower drains.

On the other hand, if sewage is backing up from the basement then the problem is with the sewer line or the basement drains themselves.

Causes for Sewer Back Ups in the Basement

The following are the main causes of sewer backups in the basement:

1. Clogged Sewer Line

If you flush or dump things which you shouldn’t in your drains, they will surely clog your sewer line. If is not toilet paper or human waste then you shouldn’t flush it down the toilet.

That does not however always happen. Most people will flush wet wipes, dental floss, feminine sanitary products, family planning products etc. 

All these products have the potential to clog sewer lines and although it initially starts as a partial clog, it eventually develops into a full clog resulting in sewer back ups.

Pouring grease down the kitchen drain is another major cause of sewer lines clogs. Although some people believe pouring hot water afterward will prevent clogs, the grease will cool and solidify inside the sewer line resulting in clogs.

2. Tree Roots

Old sewer lines were made of clay or cast iron. It is not unusual for cracks to develop in these lines making the surrounding area wet.

Tree roots will naturally grow towards sources of water. If there are trees closer to where you live, the roots will start to penetrate the sewer lines through the tiny cracks and once inside due to the moisture and nutrients present they will multiply at a very fast rate.

The tree roots will start trapping solids like toilet paper and food waste and after sometime you will have a fully clogged sewer line.

3. Clogged City Sewer Lines

It is not your sewer line alone that is susceptible to clogs. If your sewer line is connected to the city’s sewer lines and not a septic tank, the sewage could be backing up to your basement from the city’s sewer lines.

It is not easy to tell for sure if the city sewer lines are clogged. Perhaps you should try and talk to your neighbors and see if they are having the same problem as yourself.

If indeed that is the case, contact your city’s drainage department and inform them of the problem.

4. Heavy Downpour

If there is sewage backing up from your basement during or after a heavy downpour, the excess water could be the problem. You see, your city’s sewer lines are designed to carry sewage from homes and surface run off after a storm.

Surface run off after a heavy downpour can overwhelm the public sewer lines forcing it plus the sewage already in the lines to back up through your basement.

How to Stop It

The following are the steps you should follow to stop sewage back up in the basement:

1. Turn off the Water

Unless the problem is caused by a clogged city sewer line or heavy downpour, turning off the water in your house ensures that you will have no more sewage backing up.

To turn off the water to your house, locate the main shut off valve. The shut off valve is usually located in the basement very close to the water heater. It could also be located on an exterior wall where the service line enters the house.

Even after turning off water, there is still water in the lines and toilet tanks. Inform everyone in the house of the problem at hand and that nobody should flush the toilet.

2. Turn off the Power

If the basement is flooded, it is very important that you turn off power to that specific area until the problem is resolved. If the problem is not that severe however you can let it be.

As I mentioned, sewage can make you sick even when not ingested. Dress appropriately for the job to make sure that your body does not come into contact with it.

At this point, you should make a decision of whether you want to fix the problem yourself or you want a professional to have a look.  You should also determine if the problem is only affecting one drain or it is all the drains which means a clog in the sewer line.

If you want to fix the problem on your own proceed as shown below.

How to Fix It

If you want to unclog a sewer line on your own, you will need the following:

  • A drain snake
  • Wrench
  • PPE

1. Locate the Sewer Cleanout

A sewer cleanout is a vertical pipe connected to the sewer line very close to the house that gives you access to the sewer line. It can either be found inside the house (in the basement) or outside.

If the sewer cleanout is installed outside the house, it will be sticking out a few inches from the ground and has a cap with a square nut at the top.

Since sewer lines drain to the public sewer lines on the street, the sewer cleanout will be found on the side of the house facing the street. It may not be easy to locate since most homeowners try as much as possible to hide them.

If there are flower bushes around the house, that is where you are most likely to find it. Sometimes it can be completely buried under mulch.

Sewer cleanouts inside the house form a “T” OR “Y” with the main drainpipe but could still be hidden so be sure to open closets and any decorations resting against the wall.

2. Remove the Sewer Cleanout Cap

Grab the square nut on the cleanout’s cap using a wrench and slowly turn it counterclockwise to loosen it. If you hear any pressure leaking out wait until it stops.

You do not want to open the cap fast since the sewage can splash all over your face. This should however not happen in this case since there is no sewage in the drain stack to exert pressure.

3. Snake the Sewer Line

You cannot snake a sewer line using the ordinary drain stake. You need a motorized drain snake which is both long and strong.

Since you are not likely to have that type of snake lying around in your garage, you can rent one from a nearby plumbing store. The drain snake will come with different sizes of blades.

Start by connecting the smallest size of blade and pushing it down the sewer line. As you push the snake in the sewer line, you need to be careful to make sure that you are pushing it in the actual sewer line and not back inside the house drain.

The drain snake blades will cut through whatever that is clogging the sewer line and pull it out. Connect the next size of blade and put it back to completely clean the sewer line.

The advantage of hiring a professional instead if fixing the problem yourself is that they have a sewer camera which they will first run to determine the status of the sewer line (to check if it is failing) and also check the type of clog to determine which blade to use.

Put back the sewer clean cap after unclogging the sewer line.

Don’t Have a Sewer Cleanout?

If you do not have a sewer cleanout in your house, there is something else you can do although it is a lot of work and with a lower success rate.

You can either access the sewer line from the plumbing vent or the toilet drain. The reason a toilet drain is preferred is because unlike tubs and sinks, a toilet drain is bigger in diameter (usually 4-inch) and is connected directly to the drain stack.

You will however need to remove the toilet in order to snake the sewer line without damaging the inside of the bowl.

If you do not want to remove the toilet, you can climb to the roof of the house and snake the sewer line from the plumbing vent.

Clean Up After a Basement Sewer Back Up

After unclogging the sewer line, the next thing you will need to do is to clean up the basement to make the house safe to live in, prevent water damage as well as keep mold and mildew at bay.

The first thing will be to remove standing water using towels (that are you are happy to throw away) and/or wet dry vacuum. When the water has been removed, collect all the affected solids that cannot be salvaged and trash them.

After removing standing water and solid waste, it is now time to disinfect the basement to kill the germs still left on surfaces.

Start by cleaning every inch of the affected area using warm water and soap. Next use a mixture of bleach and water to wipe down all the surfaces in order to disinfect them. It is a lot of work but you must do it to protect your family.


The following are some of the ways you can use to prevent your sewer line from clogging and sewage backing up from the basement:

  • Don’t flush what you should not flush down the toilet. If it is not toilet paper or human waste then just don’t do it.
  • Do not pour grease down the drain. The grease will coalesce and badly clog the sewer line especially when it combines with other substances in the wastewater.
  • Don’t plant deep rooted trees near the sewer lines. Tree roots are among the top causes of clogged sewer lines. If the trees are already there you can plan to have the rots cut from time to time.
  • Have your sewer line checked by a drain specialist at least once a year.
  • Install a plastic sewer line. Unlike cast iron and clay pipes, plastic pipes do not corrode and do not crack, inviting tree roots.

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