What to do about a smelly drain inside your house
You walk into the house, and there it is. That smell.
It might come and go.
It might linger around the kitchen sink.
Or suddenly hit you upstairs in the bathroom.
Wherever it is, a smelly drain inside the house is more than just unpleasant. It's usually the sign that something's gone wrong.
Here's the tricky part:
The smell isn't always coming from where you think it is.
It's one of the most common complaints heard.
A quick word about safety.
When training for confined space work, like entering a cesspit or chamber, specialist gas detectors are used for a reason.
Drain smells aren't just unpleasant. They can contain dangerous gases like:
-
Hydrogen sulfide
-
Methane
-
Ammonia
At low levels, these gases can cause headaches and nausea.
At high levels or with long exposure, they can affect your breathing or worse.
If you can't get the issue looked at straight away, leave a window open overnight.
Don't just spray air freshener, get curious.
When called to one of these jobs, the first thing checked is simple:
The vent system.
Smells are meant to escape safely up the soil vent pipe, not back into your home.
But if the vent is:
- Blocked by debris (yes, even birds' nests!)
- Missing entirely (common in older properties)
Then those smells have nowhere to go but back indoors.
Private systems make a big difference.
Next question:
- Is there a pumping station?
- Is the property on a private treatment plant or septic tank?
If these aren't maintained or emptied properly, gas can back up, especially if:
- The filters are clogged
- The tanks are full
- The vent isn't working as it should
One job never forgotten.
A house was called out to where the customer was sure the smell was coming from the upstairs toilet.
She was convinced, and honestly, it was easy to see why.
It smelled like that was the issue.
But when investigated, the problem was actually under the bathroom floorboards.
A cracked pipe, leaking just enough to release gases, but not enough to cause a visible mess.
A smoke test was used to trace it.
Quick fix. Smell gone.
Why the smell might be worse at certain times.
Some customers say, "It's only bad in the morning," or "after I run the washing machine."
That's a useful clue.
Why? Because:
- When the system is disturbed (like flushing or draining), gases can get pushed into the home.
- If the vent pipe's blocked or missing, those gases find the weakest point, often under a sink or bath.
If you've got a pumping station, it's even more likely.
Gases build up. If there's nowhere else to go, they come back into the house.
What gets checked when you call ASL Limited out.
At ASL Limited, smelly drains inside houses are dealt with all the time.
Here's how the investigation happens without pulling the place apart:
- Smoke tests, great for detecting cracks in hidden pipework
- Visual checks, gully traps, vent pipes, overflows
- Private systems, checking for pumping stations, treatment plants, or septic tanks nearby
- Water tests, tracking slow drainage or minor leaks
- Check for missing traps, often under sinks, baths, or unused showers
- Cold-weather checks, some smells come from pipe movement or poor insulation
Every house is different. But once the source is found, the fix is usually simple.
What you can do before calling.
If you want to narrow it down before calling out, here's what to try:
- Run water down each sink or bath. If the trap's dry, smells can escape.
- Test appliances, does the smell get worse after the dishwasher or washing machine?
- Think back, any recent plumbing changes? A missed vent or cracked pipe might be to blame.
Don't guess, get it checked.
Indoor drain smells can cause stress, embarrassment, and even health concerns.
No one wants to live with that, especially if you're selling or renting the home.
The good news?
Once the source is traced, it's usually quick and affordable to fix.
Got a smell you can't trace?
Let's find it and sort it.
📞 Call ASL Limited on 0800 181 684. The experience and the tools are available to deal with it fast.
We cover Surrey, Berkshire, Hampshire, West Sussex and South West London.
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To learn more about how ASL Limited can help with smelly drains:
