You walk down to your basement expecting to grab something from storage—and suddenly you’re hit with a strong, foul odour that smells like sewage. If your basement smells like sewer gas, you’re not alone. Many Toronto homeowners experience this unpleasant surprise at some point, and while it’s often not immediately dangerous, it’s a clear sign something’s wrong in your plumbing system.
There are a number of frequent causes for sewer odours in basements, including broken or clogged pipes, dried-out drain traps, or even damaged sewer lines. Left unresolved, it can worsen over time and may even pose health risks due to exposure to sewer gases.
In this blog, we’ll explain why your basement smells like sewage, the most common causes behind it, and what you can do to eliminate sewer odours. You’ll also learn when it’s time to call in professional plumbers in Toronto, such as the trusted experts at Absolute Draining & Plumbing, who have over 20 years of experience keeping homes safe, clean, and odour-free.
Notice a sewer smell in your basement? Don’t wait for it to get worse—contact our certified plumbers in Toronto, Etobicoke, or Mississauga for fast, reliable drain and plumbing solutions.
Why You Might Smell Sewage in Your Basement
A sewage smell in the basement often points to an issue somewhere in your plumbing or drainage system. The odour usually comes from sewer gas—a mix of methane, ammonia, hydrogen sulfide, and other gases that form as waste decomposes in your sewer line.
While small amounts of sewer gas may not cause harm, constant exposure can affect your indoor air quality and lead to headaches, nausea, or dizziness. Beyond the health concerns, the stench alone is enough to make any basement unbearable to use.
Let’s explore what might be causing that persistent sewer odour.
1. Dried-Out or Unused Floor Drains
One of the most common causes of sewer gas smell in basements is a dried-out floor drain. Every drain in your home is designed with a P-trap, a curved section of pipe that holds a small amount of water. This water trap acts as a barrier, preventing gases from travelling up from the sewer into your living spaces.
When a drain hasn’t been used for a while—especially in basements or laundry rooms—it can evaporate. Without that seal, the gases have a clear path to enter your home, resulting in that unmistakable foul sewer smell.
How to Fix It:
- Pour water into the drain. Start by running a few litres of water into your floor drain to refill the trap.
- Add a bit of cooking oil. Pouring a thin layer of oil after the water slows down evaporation.
- Use drains regularly. Make it a habit to run water into unused drains every few weeks to maintain the seal.
If the smell persists even after doing this, you may be dealing with a clogged drain trap or a damaged seal, both of which require professional attention.
2. Clogged or Dirty Floor Drains
Another culprit behind foul odours in basements is a clogged drain. Over time, dirt, debris, soap scum, and other waste build up inside the drainpipes, restricting water flow and trapping organic matter that starts to decompose.
The blockage not only slows down drainage but also traps moisture and bacteria—an ideal environment for foul odours to form.
How to Fix It:
- To break down scum and eliminate bacteria, flush the drain with hot water diluted with baking soda and a little amount of white vinegar.
- Avoid harsh chemicals, which can damage your plumbing system and the environment.
- To completely clear the line, hire a qualified plumber to do a drain cleaning utilizing hydro-jetting or an auger if the obstruction is severe or long-lasting.
At Absolute Draining & Plumbing, we use advanced tools to remove stubborn blockages safely without harming your pipes.
3. Broken or Missing Cleanout Plug
Your basement floor drain usually has a cleanout plug—a removable cap that allows plumbers to access the main drain line for maintenance or cleaning. Sewer gases may leak into your basement if that plug breaks or disappears.
This issue is often overlooked because the plug is located deep inside the floor drain and not visible at first glance.
How to Fix It:
If you suspect the cleanout plug is missing, remove the grate covering your floor drain and inspect the interior. If you notice an empty opening or a broken piece, contact a licensed plumber in Toronto to replace it properly. It’s a quick fix, but it must be done right to ensure a tight seal.
4. Cracked or Damaged Sewer Lines
Sewage odours might also be released by a broken or fractured sewer line. These pipes transport garbage to the municipal sewer and run outside your house or under the basement floor. When they crack due to age, shifting soil, or tree roots, sewage can leak into the ground—and the gas that escapes can find its way indoors.
In some cases, you may notice not just odours but also slow drains, gurgling sounds, or even damp spots on your basement floor.
How to Fix It:
Fixing a broken sewer line isn’t a DIY job. A professional drain inspection using a camera is the best way to pinpoint the exact location of the damage.
At Absolute Draining & Plumbing, our team uses no-dig (trenchless) repair technology to seal cracks and replace damaged sections without tearing up your property. Depending on the situation, we may use epoxy lining or hydraulic pipe bursting to restore your sewer system efficiently.
5. Sewer Ejector or Sump Pump Issues
Ejector pumps are frequently used in homes with laundry rooms or basement bathrooms to pump wastewater upward into the main sewage system. Sewage gas may begin to smell if this system isn’t adequately sealed or vented, or if the lid or gasket is broken.
Similarly, a sump pump pit can trap stagnant water, producing a musty or sewage-like odour if not cleaned regularly.
How to Fix It:
- Check if the ejector pump cover is securely sealed.
- Make sure the vent pipe is connected and unobstructed to allow proper airflow.
- If the pump is old or malfunctioning, contact a plumber for repair or replacement.
Our Toronto team specializes in sump pump repair and maintenance, ensuring your basement stays dry and odour-free.
6. Problems with Vent Pipes
Your plumbing system has vent pipes that balance air pressure and allow gases to escape through the roof instead of your home. If a vent pipe is blocked—often by debris, leaves, or even snow during winter—it can force gases back into your home through drains.
How to Fix It:
- Listen for gurgling sounds when flushing toilets or draining sinks—this often signals venting issues.
- You can try running water in nearby fixtures to see if the smell dissipates.
- For safe and thorough cleaning, a professional plumber should inspect and clear the vent line from the roof.
7. Leaky Seals or Wax Rings Around Toilets
Sometimes the sewer odour in your basement doesn’t come from the drains at all, but from your toilet flange seal. Over time, the wax ring that seals the base of your toilet to the drain pipe can dry out, crack, or shift, allowing sewer gases to escape.
How to Fix It:
If you notice odours around a basement toilet, gently rock the fixture—if it moves, the wax seal is likely compromised. A plumber can replace the wax ring or install a new flange to restore the airtight seal and eliminate odours.
8. Clogged or Backed-Up Main Sewer Line
If several drains throughout your home are slow or you hear gurgling noises, the issue might be with your main sewer line. A blockage here can cause wastewater to back up through your floor drains, carrying both odours and contamination.
How to Fix It:
Professional plumbers perform a camera inspection to confirm a main line clog. Once identified, they’ll use hydro-jetting to clear grease, roots, and debris from the line.
Absolute Draining & Plumbing offers flat-rate pricing and 25-year warranties on drain repairs, giving Toronto homeowners long-term peace of mind.
If your basement smells like sewage, it’s time to act. Book a plumbing inspection in Toronto, Etobicoke, or Mississauga and restore your home’s comfort today.
The Role of Routine Plumbing Maintenance
Preventing a basement sewer smell starts with regular maintenance. Homeowners often overlook basement drains or sump pits simply because they’re out of sight. However, staying proactive saves you time, stress, and repair costs down the line.
Practical Solutions & Maintenance Tips:
- Run water into unused drains every few weeks to keep traps sealed.
- Inspect sump and ejector pumps annually for leaks or odours.
- Schedule professional drain cleaning at least once a year to prevent buildup.
- Avoid pouring grease, oil, or food scraps down your drains.
- Check vent pipes after storms or heavy snow to ensure they’re clear.
- Watch for early warning signs like slow drains, bubbling toilets, or persistent damp smells.
Routine inspections from experienced plumbers ensure your plumbing system stays in top shape and help you catch small issues before they turn into major repairs.
Health and Safety Concerns: Why Sewer Gas Isn’t Just an Inconvenience
Aside from the unpleasant smell, prolonged exposure to sewer gases can have serious health effects. Hydrogen sulfide, even at low levels, can cause irritation, headaches, or nausea. In higher concentrations, it may become toxic.
If you ever experience dizziness or difficulty breathing in a space with a strong sewer odour, leave the area immediately and call a professional for emergency assistance.
Sewer gas also poses explosion risks since methane is flammable. This is another reason it’s crucial to deal with any persistent sewer smell in the basement as soon as you notice it.
When It’s Time to Call a Professional Plumber for Basement Sewer Smell
You can handle small plumbing issues like dried-out traps yourself, but if the smell in your basement keeps coming back—or if you suspect a broken sewer line, vent blockage, or sewage backup—it’s time to call the professionals.
At Absolute Draining & Plumbing, our licensed plumbers have been serving Toronto and the GTA for over 20 years. We use video inspections, trenchless repair methods, and hydro-jetting to pinpoint and solve odour problems efficiently.
We also assist homeowners with plumbing rebates, provide flat-rate pricing, and guarantee our drain repair services for up to 25 years. Whether you’re in Etobicoke, Mississauga, North York, or downtown Toronto, we’re available 24/7 for emergency plumbing services.
How Absolute Draining & Plumbing Can Help
Here’s how our expert plumbing team can help eliminate that foul sewer smell in your basement:
- Comprehensive inspections: Using camera technology to locate leaks, cracks, or clogs.
- Drain and sewer cleaning: Clearing buildup safely and effectively.
- Trenchless sewer repair: Fixing damaged lines without digging up your property.
- Sump and ejector pump maintenance: Ensuring sealed systems and proper drainage.
- Backwater valve installation: Protecting your basement from future sewage backups.
- Waterproofing solutions: Preventing moisture and odour problems caused by leaks.
Our mission is to help Toronto homeowners breathe easier, knowing their homes are protected from sewage odours and plumbing failures.
Keep your home safe and odour-free. Contact our plumbers today in Toronto, Etobicoke, or Mississauga to inspect, repair, or prevent sewer smell in your basement before it becomes a bigger problem.
Eliminate Sewer Smells in Your Basement for Good
A sewage smell in the basement is more than a nuisance—it’s a warning sign from your plumbing system. Whether it’s a simple dried-out trap or a cracked sewer line, identifying the cause early prevents costly damage and keeps your family safe.
If you’re tired of that persistent sewer odour in your home, don’t wait for it to get worse. Call Absolute Draining & Plumbing today at 416-252-5557 or request a free estimate online.
Our Toronto plumbing experts will inspect your system, locate the source of the problem, and provide lasting solutions to eliminate sewer gas smells and restore comfort to your home.
