Sewer Smell in the House: Where It Comes From and What to Check

Oliver Owens
Apr 21
6 min read

Sewer smells are not normal, even if they show up once and disappear

Most homeowners describe it the same way. A rotten egg smell in the bathroom that comes and goes. A weird odor near the laundry room after the washer drains. A smell under the kitchen sink that is stronger at night, then seems fine in the morning.

Whatever the pattern, sewer smell is your house telling you something is off. Sometimes it’s a simple fix, like a dry drain trap in a bathroom you barely use. Other times it’s an early warning sign of a bigger drain or sewer problem.

At Kramer’s Plumbing, we troubleshoot sewer smells in Placentia and across North Orange County all the time. This guide walks you through the most common causes, what you can check safely, and when it’s time to call a plumber before it turns into a backup.

First, what does a sewer smell actually mean?

That rotten egg odor is commonly linked to hydrogen sulfide, which is a gas that can be associated with sewage systems. It’s known for that distinct smell at low levels, and exposure can irritate the eyes and respiratory system.

In most homes, you’re not dealing with a dangerous concentration. But you still want to take sewer odor seriously because it can signal a plumbing issue that can worsen, and because gases can build up in poorly ventilated or low areas.

One important note: smell is not a perfect safety indicator. With hydrogen sulfide, your sense of smell can fatigue, which is one reason you should not ignore ongoing odor problems.

The most common causes of sewer smell in a house

1) A dry P trap

That U shaped pipe under your sink is not just plumbing, it’s a seal. It holds a small amount of water that blocks sewer gases from coming up through the drain.

If a sink, shower, or floor drain is rarely used, that water can evaporate. Once the trap dries out, odor can come right into the room.

Where we see this most:Guest bathrooms, floor drains in laundry rooms, and tubs that do not get used often.

2) Buildup inside the drain

Sometimes what you’re smelling is not sewer gas from the main line. It’s bacteria, food residue, and sludge living in the drain or overflow channel.

This happens a lot in:Bathroom sink overflows, kitchen drains, and laundry standpipes.

3) A toilet wax ring that is failing

Your toilet has a seal at the base that keeps sewer gas where it belongs. When that seal fails, odor can leak around the toilet base, especially after flushing.

Clues:Smell is strongest near the toilet, the toilet rocks, or you see moisture or staining at the base.

4) A venting issue

Your plumbing system needs venting to balance pressure and direct gases out through the roof vent. If a vent is blocked, damaged, or improperly vented, you can get gurgling, slow drains, and sewer smells.

Homeowner clue:Gurgling plus odor, especially when multiple fixtures run.

5) A partial sewer line restriction

If sewer odor shows up along with slow drains, gurgling, or occasional backups, you may be dealing with a developing main line clog. This is the one you do not want to ignore.

If you want to understand the warning signs before a backup happens, link this companion post once it’s live: Main Sewer Line Clog Warning Signs Before a Backup Happens

6) Grease buildup and kitchen drain issues

Kitchen lines are notorious for grease buildup. Even small amounts of fats, oils, and grease can accumulate over time and contribute to clogs and odors. Orange County Sanitation

District specifically warns that FOG buildup leads to clogs and overflows, and they recommend collecting it in a container and putting it in the trash.

What to check first, safely, before you call

You can usually narrow sewer smell down with a simple process.

Step 1: Identify the strongest location

Do a quick walk and pay attention to where it’s strongest:

Bathroom sink
Toilet base
Shower or tub drain
Laundry room
Under the kitchen sink

This matters because sewer smells are often very localized.

Step 2: Run water in rarely used drains

If you suspect a dry trap, run water for 30 to 60 seconds in the sink, tub, or floor drain. Then give it 10 to 15 minutes and see if the smell improves.

If it improves, you likely found the cause.

Pro tip for rarely used drains:Running water weekly keeps the trap seal in place.

Step 3: Clean the drain and overflow

For bathroom sinks, clean the overflow opening because that area can hold residue that stinks.

For kitchen drains, flush with hot water and mild soap, and clean any removable strainers.

If the smell is still present after cleaning, it may not be surface buildup.

Step 4: Check under sinks for leaks and trapped gunk

Sometimes the smell is not the sewer line at all. It’s moisture and organic buildup under the cabinet. Look for:

Dampness
Moldy smell
Drips at the trap connections
Standing water in the cabinet base

Even a small drip can create a nasty odor over time.

Step 5: Check the toilet for wobble

Gently test if the toilet rocks. If it moves, the wax ring seal may be compromised, which can let sewer gas escape.

Do not keep using a rocking toilet. It can worsen the seal and lead to water damage.

Step 6: Pay attention to symptoms that suggest a main line issue

If you have sewer smell plus any of these, stop the DIY loop and call:

Multiple drains slow at once
Gurgling toilets when other fixtures run
Water rising in the shower when the toilet flushes
Repeated clogs within weeks

That pattern is often a main line restriction, not a simple local issue.

What not to do

Do not pour chemical drain cleaners down the line

We know why people try them. It feels like the quickest fix.

But drain cleaners contain very dangerous chemicals and can harm you if swallowed, inhaled, or if they contact skin or eyes. They also make professional drain clearing riskier if chemicals are still sitting in the line.

If odor is caused by a dry trap, a wax ring issue, venting, or a main line restriction, chemical drain cleaner does not solve the real problem anyway.

Do not ignore a smell that keeps coming back

A one time odor after a long vacation might be dry traps. A recurring odor often has a mechanical cause that will not fix itself.

When it’s time to call Kramer’s Plumbing

Call if:

Sewer smell persists after you run water and clean drains
Odor is strongest at the toilet base, or the toilet rocks
Odor comes with gurgling, slow drains, or backups
You suspect a venting issue
The smell is strongest in the laundry room and the standpipe gurgles

When we diagnose sewer smells, we’re not guessing. We identify whether the issue is a trap seal, a toilet seal, a drain condition, venting, or a sewer line restriction, then we give you the right fix for that specific cause.

What you can expect during a professional diagnosis

Depending on symptoms, we may:

Inspect traps and connections for leaks
Check toilets for proper sealing and stability
Evaluate venting symptoms
Clear and clean lines when buildup is the root cause
Recommend a camera inspection if the pattern points to the main line

The goal is to stop the smell and prevent the next problem, not just mask it.

FAQ: Sewer smell in the house

Is a sewer smell dangerous?

Sewer odors should be taken seriously. Hydrogen sulfide exposure can irritate the eyes and respiratory system, and in higher concentrations it can cause serious effects. In homes, the bigger point is that odor often signals a plumbing problem that can worsen.

Why does it smell worse at night?

Lower water use can let traps dry out, and airflow patterns can change. Odor can also be more noticeable when the house is closed up.

Can a dry drain really cause sewer smell?

Yes. The water in the trap is the seal. If it evaporates, sewer gases can come through.

How do I know if the toilet wax ring is the problem?

Smell is strongest near the base, the toilet rocks, or you see moisture or staining.

Why do I smell it after running the washer?

Laundry standpipes can have trap or venting issues, and washing machine discharge can push air around in a restricted line.

Should I use bleach or chemicals to fix the odor?

We don’t recommend chemical drain cleaners. They can be hazardous and often do not address the true cause.

Can grease cause sewer smell?

It can contribute, especially in kitchen lines. Local wastewater guidance warns that fats, oils, and grease build up in pipes and lead to clogs and overflows.

When should I call a plumber?

If the odor persists after basic checks, or if it comes with slow drains, gurgling, or backups.

Call Kramer’s Plumbing for sewer odor diagnosis in Placentia, CA

If sewer smells keep coming back, let’s find the real cause and fix it the right way. Kramer’s Plumbing is based in Placentia and serves North Orange County including Fullerton, Brea, Yorba Linda, Anaheim Hills, and Chino Hills.

Call (714) 260 3986 or book online here.