Why Does My Chicagoland Basement Smell Like Sewage? Bad Sewer Smell Causes & When to Call Your Local Plumber

Your home in the Chicagoland area is your sanctuary, and it deserves to be pristine and welcoming. However, if you enter your basement and are greeted by the scent of sewage, you’re falling short of that aspiration.

Why Does My Basement Smell Like Sewage? 

When your basement smells like sewage, two of the most common reasons could be due to a dry P-trap or loose cleanout cap, which allows sewer smells to constantly leak out. 

The good news is that a basement sewage smell can almost always be solved through DIY methods. 

Some you can fix in five minutes with a pitcher of water. Others might require a quick drive to your local hardware store and buy a $10 replacement. But on some occasions, you need a licensed plumber. 

Before doing anything too drastic, we’ll run you through the 6 most common causes, how to fix each one, and when it’s time to call in a professional. 

The 6 Most Common Causes of Sewer Smell 

1. Dry P-Trap

This is the first thing to try.

Every floor drain and basement sink has a P-trap (a U-shaped section of pipe that holds water to block sewer gas from rising). If that drain has not been used in a few weeks (2 to 4 weeks average), the water evaporates and the seal disappears.

Think of the water as a shield against sewer gas. If you haven’t used them in a while, the water evaporates and gases are able to escape more easily.

You probably have several P-traps around your home, starting with your kitchen sink, laundry, and shower. 

How to fix it:

Pour two to three cups of water down any floor drains you have not used recently. Add a tablespoon of mineral oil on top to slow evaporation. If the smell clears within a few hours, you’ve confirmed the problem was your P-trap.

2. Missing or Loose Cleanout Cap

Check the floor drain bowl first.

Inside the drain opening, there should be a cleanout plug: a small cap that creates a secondary gas seal. These get removed during drain cleanings and do not always get replaced. 

Even if they’re slightly loose, gases can still easily escape. 

How to fix it: 

If the plug is missing or sitting loose, there is a direct gas pathway into the basement. A replacement cap costs under $10 at any hardware store and installs in minutes.

3. Failed Wax Ring

The wax ring seals the base of your toilet to the drain pipe.

When it wears out or shifts, sewer gas escapes around the toilet base. The tell-tale signs are: 

• A toilet that rocks when you sit on it
• Water pooling at the base after flushing, or; 
• You notice the smell is strongest right near the toilet

How to fix it:

This is not a great DIY job for most homeowners since the toilet needs to be fully removed, the old wax completely cleared, and the new ring seated correctly. In the DuPage County and Chicago area, a licensed plumber typically handles this for $75–$250, depending on what is found during the repair.

4. Blocked Vent Stack

Your plumbing system vents sewer gas through a pipe that exits through the roof.

When leaves, debris, ice, or a bird nest block that vent, gas has nowhere to go and gets pushed back into the house. The giveaway is usually gurgling sounds when you flush, slow drains across multiple fixtures, or a smell that worsens after heavy water use. 

How to fix it:

Clearing and inspecting the vent stack safely requires a plumber with the right roof access and equipment.

5. Leaking Sump Pump

Every sump pump comes with a pit mainly for collecting wastewater. But if the basin is unsealed, or filled with a lot of debris, you get a basement that smells like the sewer.

If you’d like to check whether your sump pump is still in good condition, check out our guide on 6 Sump Pump Failure Signs to Watch Out For

How to fix it: 

Make sure the sump pit is sealed tight, and clean out any debris. Then, do a quick test: pour water into the sump pit to make sure it’s sealed properly.

6. Cracked or Damaged Sewer Line

This is the one to catch before it gets worse.

When a sewer pipe cracks, from age, shifting soil, or root intrusion,  gas escapes through the break and works its way up through the concrete slab. You may not see water. The smell appears first, sometimes faint and intermittent.

Left alone, the crack expands. 

How to fix it. 

A basement sewage smell from a hairline crack is a very different repair than one from a full line failure. A camera inspection or calling a plumber is the only reliable way to know what is happening underground.

DIY vs. Call a Plumber: Quick Reference

Use this to triage the problem before picking up the phone.

Sewer Smells are More Common in Older Homes

Older homes across Wheaton, Naperville, Glen Ellyn, Downers Grove, Elmhurst, and the surrounding DuPage County suburbs frequently have original clay sewer lines still in service.

Clay holds up well for decades, but it cracks at pipe joints over time, and DuPage County is tree-heavy. 

Root systems in neighborhoods with mature oaks and maples actively seek out moisture and find their way into those joints. If your home was built before 1980 and the sewage smell has come back more than once after refilling the P-trap, a sewer camera inspection is the fastest way to rule out a line problem before it becomes a much larger repair.

A Warning Note on Sewer Smells – (When to Call Your Local Plumber)

Sewer gas is heavier than air.

It sinks to the lowest level of the house, which is why basements catch it first. The smell comes from hydrogen sulfide, the chemical behind that rotten egg odor, along with methane and ammonia produced by decomposing waste in your sewer system. 

However, in some cases, the smell can cause nausea and headaches. Worse, if the sewer gases come in contact with moisture, you’ll have two problems: sewer smells and mold. 

When to Call a Plumber Right Now

If multiple drains are backing up at the same time, sewage is coming up through floor drains, or the smell comes with wet spots in the yard or along the basement wall, call a plumber immediately. 

There’s a high chance these point to a main line failure, not a dry trap.

The same applies if anyone in the house is experiencing headaches, nausea, or dizziness near the basement. Ventilate the space and call a plumber immediately.

• Multiple drains backing up simultaneously across the house
• Sewage coming up through floor drains or basement fixtures
• Wet spots in the yard directly over the sewer line path
• Symptoms, headache, nausea, or dizziness, in people spending time in the basement

Schedule a Sewer Line Plumbing Service With ARCO Plumbing

If you have worked through the DIY checks and the basement sewage smell is not going away, ARCO Plumbing serves Wheaton, Naperville, Downers Grove, Elmhurst, Lombard, Glen Ellyn, Lisle, and Bolingbrook. 

Call us at 630-960-5950 to get your sewer line checked ASAP, or schedule a service appointment via our website today.