Sewage Backup in Basement: Causes and Fixes

Sewage backup in basements is at or near the top of most homeowners’ worries. The pipes are hidden in walls, ceilings, under the basement floor, and underground, making it difficult to monitor their condition. So, even though many insurance companies offer protection against sewage backup, that doesn’t alleviate the concern. However, knowing what can cause a backup and how to prevent or fix one may prove helpful.

Household sewer lines can clog and back up if non-bodily waste and items are flushed or allowed to go down the drain. Other causes can be tree roots, older pipes, heavy rains, ground movement, or failure in the municipal line. Making sure home occupants know what can and shouldn’t go down the drain is the best prevention, as are pipe inspections and installing a backflow valve.

In this article, we’ll identify signs of sewage backup, their causes, prevention, and fixes. We’ll explain how to clean up a backup, the best cleaning product, potential costs, health risks, and how long the contamination can last. We’ll also discuss homeowner’s insurance regarding sewage backup, and whether municipalities can be held accountable for damages. Our aim is to provide you with the information to address the possibility before it becomes an issue.

Sewage Backup in Basement

What Are Signs of Sewage Backup?

A sewage backup doesn’t normally happen out of the blue. There are often signs that all is not right on the path to the cesspool, treatment facility, or septic tank. The longer the signs are ignored, to worse the problem can become, and the more potential for a damaging backup. Here are ten common signs to be aware of when determining if your blackwater drain pipe is plugging up.

  • Bubbling toilets, sinks, and tubs or showers can be an indicator that there is a blockage somewhere along the line. Wastewater that isn’t able to freely drain can trap air, which produces bubbling in toilet bowls and sink drains.
  • A toilet backing up or overflowing commonly means it is clogged, but it could also indicate that there is a sewage line blockage.
  • Animals and insects are attracted to the smell of sewage and may dig or burrow where pipes are leaching. This often indicates that there is a problem that needs to be addressed. This is more common with septic fields but is especially telling if it occurs close to the house or on municipal sewers.
  • Changes in the lawn where the sewer pipe goes to meet septic tanks or sewer lines. A clog can cause seepage into the ground at pipe joints and the moisture can cause the soil to sink or mound up, become wet, or even smelly.
  • Strange, unusual, or nasty sewage-like odors emanating from sinks and drains other than the kitchen sink. Kitchen sinks commonly produce odors but drains in tubs, showers, and other sinks seldom do. So smells from them are a good indicator that something isn’t right in the sewage system.
  • Slow-draining sinks or tubs often indicate a blockage in their location which can be easily cleared in different ways. However, if the drain has been cleared and is still slow, or there are multiple drains that become slow at the same time, then there is likely a blockage further down the pipe.
  • Water backing up into tubs or sinks when a toilet is flushed or another drain is released is a good indication there is a clog in the sewage line.
  • Water or sewage seeping from the cap of the sewer cleanout pipe which is located in the basement or outside the house is a good indicator of a blockage.
  • If you experience some of the other issues, consider removing the sewer cleanout pipe cap and looking to see if there is water visible in the pipe. Standing water in the cleanout pipe is an indication that there is a drainage issue.
  • Cracks in the foundation can be caused by pressure due to sewage backup, although they are usually caused by other issues. Either way, this is something that should be checked out.

What Causes Sewer Backup in the Basement?

What Causes Sewer Backup

There are many reasons a sewer backup can occur. Some are human error or carelessness. Others wear and tear and age, and a few can be laid at the doorstep of Mother Nature. The following are some of the reasons sewer backups can occur.

1. Household Pipe Clogs

Household sinks, tubs and showers drain into 1-1/4” to 2” diameter pipes that commonly join a larger diameter wastewater pipe inside the house. Toilets and basement floor drains directly connect and flow into the larger diameter pipe.

The household sewage pipe has a smaller diameter than municipal sewers and is more likely to clog or cause backups than the municipal line. Homes that are connected to septic tanks typically have pipes of similar diameter to the household wastewater pipe connecting them to the septic tank.

Clogs are typically caused by something being flushed down the toilet or poured down the drain. Grease, vegetable matter, food waste, paint, oil, hair, dental floss, and even toothpaste going down the sink drain can get stuck or build up over time and narrow the inner diameter of pipes.

The buildup slows the flow through the pipes, leading to larger blockage which can cause a sewage backup. Flushing food waste, baby wipes, diapers, paper towels, tampons, sanitary pads, IUDs, and even condoms down the toilet can clog or block the sewer pipe and cause a backup too. The only thing that should go down the toilet is human waste and toilet paper.

2. Heavy Rain

Heavy rains can cause problems for municipal treatment systems, to which many homes are connected. If the rains are severe enough and the system’s overflow can’t keep up, it can cause a backup and flood some homes with sewage.

3. Old Pipes Collapse

Modern sewer and drain lines are commonly made of ABS or PVC. However, in the past, pipes that connected the household fixtures to the sewer or septic tank were made of brick, concrete, cast iron, other metals, and even terra cotta or clay. Older pipes deteriorate over time and can rupture or collapse. They also are not as smoothly connected, so joints often are catchment areas that develop into clogs.

4. Tree Roots

Tree roots are a common cause of sewer backup, especially in areas with older pipes between the house and municipal sewer or your septic tank. Older pipes often had more joints that over time would leak, plus the pipe itself could crack and leak.

Tree roots are attracted to moist soil, so they would worm their way into the seams and cracks. Once exposed to nutrient-rich water, the roots quickly multiply. Toilet paper and solid waste get caught in the roots and cause a blockage, resulting in a sewage backup.

5. Ground Shifts

Earth tremors, blasting, heavy equipment movement, sinkholes, and even frost can cause ground shifts resulting in sewer backup. Deeper than normal frost caused by extended cold spells or uncommon frosts in traditionally warm areas can cause ground movement. Regardless of the cause, ground movement can cause pipes to crack or break, resulting in blockages that cause sewage to back up.

6. Municipal Sewer Line Clogs

Municipal sewer lines can sag or bell and also clog for similar reasons to household sewer lines and result in sewage backup. However, it typically affects more than one residence. So, if your neighbors also have the same problem, it’s likely a municipal sewer pipe blockage. If that is the case, contact the municipal office.

How to Fix Sewer Backup in Basement

How to Fix Sewer Backup in Basement

If the sewer backup is due to heavy rains or the municipal sewer being blogged or damaged, there isn’t much you can do but contact your insurance provider. If the backup is due to a clog within your property, it’s best to start by turning off your water supply to ensure no more mess occurs.

You should also contact your household insurer or check your home warranty plan. Depending on water levels in your basement, you may want to shut the power off at the panel too, water and electricity don’t mix well.

The water shut-off valve is commonly located in the basement near where the supply line enters the house or near the water pump if on a well. Water lines and toilet tanks will still contain water, so put notes on them or tell everyone not to flush. Sewer water can make you sick, so if you must walk or wade through it, wear rubber boots and a respirator or mask. You don’t want to make skin contact with the effluent or inhale or ingest pathogens.

The next step is to contact a reputable plumber unless you feel you can and want to tackle the blockage. If you’ve decided to do the task yourself, you’ll need to rent or buy a long, strong, motorized drain snake with different blade-size attachments. Borrow or buy a plumber’s wrench and buy disposable personal protective equipment (PPE) that includes goggles or a face shield. A 5-gallon pail can also be helpful in catching any material pulled out.

Locate the sewer cleanout. It may be inside or outside the house on the side nearest the septic tank or municipal sewer line. It’s typically 4” to 6” above the ground outside or connected to the main sewer line in the basement with a ‘T’ or ‘Y’ joint. It may even protrude from the concrete floor near where the sewer pipe exits the building. It has a round threaded lid with a raised, square ‘nut’ on the top.

If the house doesn’t have a cleanout, then you’ll need to remove the toilet closest in line to the side of the house where the sewer pipe leaves the building. You can run the snake down the toilet, but it will damage the porcelain finish. Alternatively, you can go up on the roof and drop the snake down the plumbing vent or stink pipe.

Wearing PPE, remove the cleanout cap by slowly turning it counter-clockwise. If air or liquid begins to hiss or bubble out, stop and wait for the pressure to release. This isn’t common, but you don’t want it erupting or splattering you or your surroundings. Once the pressure, if any is released, remove the cap and set it aside.

Connect the smallest set of blades to the snake and put it inside the cleanout pipe before starting the motor and pushing it down the pipe. Use the small blades to make a hole in the obstruction, then pull it out. Remember to turn it off before it’s out of the pipe! Put any debris into the 5-gallon bucket. Remove the small blades and connect the next size up and push it down the pipe. Repeat up to the largest blade set the pipe will accommodate.

The advantage of hiring a professional is that they know what they are doing and what to look for. Most also use a sewer camera to inspect the pipe before snaking it out to determine the type of clog. Additionally, they will use it to inspect the pipe after it is cleaned out to ensure the clog is gone.

If the clog was caused by tree roots or due to deteriorated or collapsed pipes, a plumber will recommend removing the roots, or excavating and repairing or replacing the pipe. Depending on the location of the blockage or damage, you may be responsible for the repair and replacement, or the municipality may be.

How to Clean Sewage Backup

Water in the basement can lead to the growth of mold and mildew. Sewage backup, however, can result in mold and mildew growth plus other serious health concerns. If insured against sewer backup, contact your insurance agent and let them deal with the cleanup.

Hiring professionals is often the fastest and safest way to clean up after a backup, but you can opt to do it yourself. It is recommended that those doing the task wear PPE and that children, anyone with health issues, and pets be kept away from the affected area.

The first step is to open windows for ventilation and pour small amounts of chlorine bleach into different sections of the area to slow down bacteria growth and improve the smell. Close doors and tape plastic over floor vents to prevent airborne movement to other house levels. Locate the source of the backup if it’s not obvious.

Remove the water and any excrement in the basement using rags, old towels, buckets, and a wet/dry vacuum. If the sump pump is working and isn’t connected to the sewer, it too can be used to help remove water. Once the water and excrement are taken care of, anything that has been in contact with it needs to be removed. Items that can be cleaned and disinfected can be saved in large garbage bags labeled to identify the contents. Everything else is garbage.

You may need a shovel to clean up debris and sludge. All contaminated materials and waste should be properly disposed of as soon as possible. If baseboards and drywall have absorbed moisture, the affected sections should be cut out, removed, and scrapped. Flooring, underpad, and affected carpets should be removed and wrapped or bagged for immediate disposal.

With the water, excrement, and removable and contaminated items out of the basement, it is time to clean and disinfect all affected surfaces. Clean all surfaces with warm to hot water and low-suds detergent. Then wipe everything down with a solution of bleach and water; the purpose is to disinfect all contaminated surfaces and items.

Don’t worry about saving contaminated clothes or rags. And remember to take a hot shower using an antibacterial soap or wash. It may take two or three applications before you feel and smell clean. Allow everything to dry before beginning repairs or returning cleaned items to the basement. You may wish to rent some industrial drying fans to speed up the drying process.

How Much Does Sewage Backup Cleanup Cost?

The cost of cleanup depends on the extent of the damage and contamination. If you’re insured or have a home warranty plan, the cost of cleanup and repairs is usually linked, and your cost is whatever your selected deductible.

Insurance companies often have a number of professional cleaning and repair companies they deal with and will recommend them. You often get to select which one you prefer. The cost of professional cleaners depends on your location and the amount and scope of the damage, and if they are also doing the repairs.

If you do the work yourself, the cost is the cleaning supplies, PPE, disposal fees, and rental cost of wet/dry vac and drying fans if required. Plus, any professional cleaning of carpets, mattresses, bedding, furniture, and any other items you hire others to clean and disinfect. A DIY cleanup alone can easily be $500 to $1,000 or more, not counting replacement and restoration costs.

Hiring a professional clean-up company can cost between $7 and $12 per square foot for cleanup and removal and proper disposal of contaminated materials. Restoration adds to that cost and will depend upon the magnitude and quality of what must be replaced. Restoration can easily surpass the cost of the cleanup.

The last flooded basement I was involved in was a 1250sqft finished basement in 2014. It was caused by an electrical outage, heavy rains, and sump pump and sewage pump failures. The water and excrement were 2” to 3” deep throughout the basement so that most of the baseboards were covered.

Unfortunately, the drywall soaked the contaminated moisture 11” up from the floor. Flooring, baseboards, doors, cabinetry, and the bottom 16” of drywall had to be scrapped to effect full cleanup. It came to over $19,000 for cleanup and restoration. The owner had to pay only the $1,000 deductible.

How to Prevent a Sewage Backup in Your Basement

The best way to prevent a sewage backup is to monitor the behavior of all drains and toilets in your home. If they experience any bubbling, strange noises, smells, slow draining, or even backup in a drain, they should be checked or cleaned out with a drain snake. If a toilet unexpectedly backs up or overflows, or there is seepage around the cleanout pipe cap, call in a professional or power snake the sewer pipe.

Other preventative measures include removing and not planting trees or shrubs near sewer lines. Make sure those using the facilities know what not to put down the drain or toilet. Replace older drain pipes or sewer lines with modern piping. Monitor lawn levels above the sewage pipe for changes and watch out for cracks developing in the foundation wall nearest where the sewer pipe leaves the building.

Hire a plumber to install a backflow valve or device that prevents sewage from backing up into the house. Also have the sewer pipe routinely inspected, or purchase an electric eye or pipe inspection camera and do your own inspections. Some insurance companies and home warranties recommend or require the sewer pipe to be inspected every 2 to 3 years, others recommend yearly inspections.

There are also dozens of products that can be poured or flushed down the drain to remove clogging material. Copper sulfate will kill tree roots inside the lines but the dead roots then need to be cut out. Organic enzyme drain cleaners will help remove fats and other debris stuck to the pipe walls and is safe for the sewer and septic tanks. Biodegradable bacteria are another preemptive method that ‘eats’ grease, fats, and even toilet paper.

Does Homeowners Insurance Cover Sewer Backup?

Homeowners’ insurance policies can cover sewer backup provided that coverage has been added to the policy prior to the backup. Some companies call it sewer backup and others sump pump or water backup. It is best to ensure that your policy covers sewer and water backup to be safe and includes sump pump failure too if you have one. The endorsement costs vary with location, insurance company, policy type, deductible, home value, and size, but usually range from $50 to $200 per year.

The endorsement typically covers damage to the home and personal property, including repair and replacement. It is important to review the fine print and follow any conditions contained in the policy to meet coverage requirements.

Some policies require an internal sewer line inspection by a professional every one to three years. The inspection may be from the cleanout to the municipal connection or septic tank, or it may include all drain lines. Payouts can be expensive, so watch out for loopholes.

Can I Sue the City for Sewer Backup?

If your home is serviced by a municipality and all legal requirements are met, you can file a legal suit against the municipality or its agents. The burden of proof, however, lies on the person filing to prove that the municipality was negligent in maintaining or providing an adequate sewer or wastewater system.

It is important to document everything, speak with neighbors who were also affected, and meet with a lawyer experienced in suit actions. In most situations where a municipal sewer failure occurs, there’s more than one household affected, leading to a class action suit.

Remember, in most municipalities the homeowner ‘owns’ the sewer pipe connecting the house to the municipal line and is responsible for its servicing and maintenance.

Sewage Backup in Basement Health Risks

The longer a sewer or drain pipe is clogged the greater the potential health risks. Water stuck in sinks, toilets, or across a basement floor longer than half a day can begin to produce toxic fumes. The type of waste in the water determines what microorganisms could be present too. If you must empty the water or immerse a hand in it, the exposure or close contact could also result in health concerns. Mold and mildew are common airborne concerns that can cause respiratory issues.

Raw sewage can cause many diseases including the virus Gastroenteritis or stomach flu, which can cause vomiting, diarrhea, fever, headaches, and cramping. It can also cause Hepatitis A, another virus, and Salmonellosis, a bacterium. Both of these can result in nausea, diarrhea, fever, abdominal pain, or cramping.

Other health risks include bacteria like E. coli, Leptospirosis, and Heliobacter Pylori which can cause intestinal issues. Sewage can even contain the presence of small amoebae, free-living microorganisms that can cause serious infections in the throat and upper respiratory system.

Other health risks due to sewer backup include electrical fires, electrocution, and Encephalitis, an inflammation of the brain. Hydrogen sulfide and carbon monoxide are also concerns that can be present if the sewer backs up. Sewage can cause serious illnesses which can easily spread and can even cause death. The effects are more serious with young children, infants, the elderly, or those who are immunocompromised.

Best Cleaner for Sewage Backup

Mrs. Meyer's Liquid Dish Soap, Biodegradable Formula, Lemon Verbena, 16 fl. oz - Pack of 3The best way to protect yourself and those living in the house is to hire professional cleaners experienced in sewage backup cleanup. If, for whatever reason, you have to do it yourself, make sure you and any helpers wear properly fitting PPE.

The best cleaner is warm to hot water mixed with a low-suds detergent for cleaning, and hot water for rinsing. It may take a couple of applications to get it clean. Follow the rinse with a sanitizing mixture of 1 cup bleach per gallon of water to disinfect all surfaces. Including those areas that weren’t in direct contact with the contaminated water.

The best cleaners to mix with warm or hot water are low-sudsing liquid detergents that cut grease. There are many on the market for sinks, dishwashers, or laundry use, but we recommend Mrs Meyers biodegradable dish soap. Chlorine bleach is the best disinfectant and is readily available in most stores.

How Long Does Sewage Contamination Last?

Contamination typically lasts until it is cleaned up. Some bacteria, such as E. coli, can last more than 100 days in water, but most bacteria exposed to sunlight usually die within 24 hours. However, most basements don’t get a lot of sunlight, so bacteria can continue to live and reproduce.

If the sewage-contaminated surfaces and contents have been properly cleaned, sanitized, and dried, contamination concerns are minimal. It should be noted though, that all surfaces in the affected area should be cleaned and disinfected, not just the contaminated surfaces.


A sewer backup is a messy, smelly, disease-causing issue no homeowner wants to experience. Those caused by heavy rains, ground shifts, or municipal sewer failure aren’t easy to predict or prevent. Having a plumber install a backflow valve on your main sewer line, however, can keep the mess out of your house. Regular inspection can identify issues with tree roots and older pipe failure, which can be removed, repaired, or replaced before they cause a bigger issue.

Backup-causing clogs in household wastewater pipes can be more easily prevented. Make sure all occupants know what can and shouldn’t be flushed or go down a drain. Watch for signs of a clog developing, and clear clogs before they cause a backup.

Insurance isn’t prevention, but it can make cleaning up and repairs after a backup less painful to your pocketbook. Hopefully, you have a better awareness of what can cause a sewage backup, how to prevent it, and how to clean it up if necessary.

Written By: Yevgen

YevgenI'm a DIY nut, and the founder and chief editor here at Weekend Builds.
This site is a result of my DIY passion, and to share the joys I have experienced fixing, building, and creating things over the years.

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