If your bathroom smells like sewer gas — especially near the toilet — it’s unpleasant and concerning. Sewer gas odors are not normal and usually mean something is allowing gases from the drain system to escape into the room.
In most cases, the cause is a loss of the water seal that normally blocks sewer gases.
Quick Answer:
A toilet smells like sewer gas when sewer gases escape past the water seal in the bowl or through a faulty connection. This is most often caused by a low bowl water level, siphoning from vent issues, a dried-out trap, or a failing toilet seal.
Why This Happens
Plumbing systems rely on water-filled traps to block sewer gases. When that water barrier is reduced or bypassed, odors can enter the home.
Common causes include:
- Low water level in the toilet bowl
- Siphoning caused by vent or drain issues
- A dried-out toilet bowl from infrequent use
- A failing wax ring or toilet seal
- Cracks or gaps at the toilet base
This problem often overlaps with a toilet bowl water level that’s too low or toilet gurgling noises, even if the toilet still flushes normally.
Step-by-Step: How to Stop Sewer Gas Smells from a Toilet
Step 1: Check the Bowl Water Level
Look at the water level in the bowl.
If it’s unusually low:
- Flush once and observe
- See if the level drops again afterward
A low water level can allow sewer gases to pass directly into the room.
Step 2: Listen for Gurgling
Flush the toilet or run nearby fixtures.
If you hear:
- Gurgling
- Bubbling
- Air movement in the bowl
…the water seal may be getting siphoned out, often due to venting problems.
Step 3: Run the Toilet Regularly
If the toilet is rarely used, the bowl water can slowly evaporate.
- Flush the toilet daily for a few days
- See if the smell improves
If odors disappear temporarily, evaporation may be part of the problem.
Step 4: Inspect the Toilet Base
Look around the base of the toilet for:
- Moisture
- Staining
- Movement when you gently rock the toilet
A failing wax ring can allow sewer gas to escape even if no water leak is visible.
Step 5: Check Nearby Fixtures
Run water in sinks, tubs, or showers in the same bathroom.
If odors worsen or water movement affects the toilet bowl, the issue may involve shared drains or vents rather than the toilet alone.
What Not to Do
- Don’t mask sewer smells with air fresheners
- Don’t ignore recurring odors
- Don’t pour chemicals into the toilet to “fix” smells
- Don’t assume odors will go away on their own
Sewer gas odors usually indicate a real plumbing issue.
When to Call a Professional
Call a plumber if:
- Sewer smells persist after flushing and cleaning
- The toilet base appears loose or leaking
- Multiple fixtures smell like sewer gas
- Gurgling and drainage problems occur together
These signs often indicate vent blockages or seal failures that require professional repair.
Safety Notes
- Ventilate the bathroom if odors are strong
- Avoid prolonged exposure to sewer gas
- Stop using the toilet if leaks or movement are present
- Address odor issues promptly to prevent larger problems
Common Homeowner Questions
Is sewer gas dangerous?
In small amounts it’s usually not dangerous, but it should never be ignored.
Why does the smell come and go?
Water levels can change due to siphoning, evaporation, or pressure changes in the plumbing system.
Will replacing the wax ring fix sewer smells?
If the seal is failing, yes — but vent and drainage issues should be ruled out first.