What to do about odours from your drains or septic system
An unpleasant smell from your drains can be a minor nuisance or a sign that something needs attention. Either way, you're in the right place.
This guide helps you identify where the smell is coming from and what to do next.
Whatever the cause, we can help you get to the bottom of it.
You notice a mild smell from one drain
If you smell something unpleasant coming from a single sink, bath, shower, or toilet — but everything else seems normal — the cause is likely minor and often something you can fix yourself.
Signs that point to a minor indoor issue:
- a rotten egg or sewage-like smell from one specific drain
- the smell is mild or comes and goes
- the affected drain is in a room that isn't used very often
- no slow drains or other symptoms elsewhere in the house
- no unusual smells outdoors
Every drain in your home has a small curved pipe underneath it called a P-trap. It holds a little water to block sewer gases from entering your house. If a drain hasn't been used for a while, that water evaporates and the smell gets through.
Debris build-up in the drain itself can also produce an unpleasant smell over time.
What to do next
In most cases, this is something you can fix yourself — no specialist needed.
Try running water down the affected drain for 30 seconds. If the smell persists, clean the drain cover and try pouring boiling water or a mixture of baking soda and vinegar down the drain.
If the smell continues after trying these steps, it's worth calling a specialist to investigate further.
The smell is persistent or coming from multiple rooms
If a foul smell lingers despite DIY fixes, or spreads to multiple drains or rooms, it's likely that something inside your system needs professional attention.
Signs that point to a more serious issue:
- a sewage or rotten egg smell from multiple drains or rooms
- the smell remains even after running water down unused drains
- the smell is stronger after heavy rainfall or periods of high water use
- mild gurgling from drains
These signs usually point to one of three causes:
- a blocked drain vent pipe — a pipe that runs through your roof to let sewer gases escape outside
- a full or overloaded septic tank that is pushing gases back through your pipework
- a drainage field that is beginning to struggle
What to do next
This needs professional attention. DIY fixes won't solve the problem.
Contact a specialist who can inspect your system, identify the source of the smell, and tell you what needs doing.
While you wait:
- reduce water use in your home where possible
- if your septic system has a control panel, note any indicators or lights
- check when the smell is strongest and where — this makes diagnosis easier
You smell a strong sewage odour outside
If you notice a sudden, especially strong smell near your septic tank, inspection covers, or drainage field, your system may be in trouble.
Signs that point to a system under serious stress:
- the ground above your drainage field feels soft or spongy
- unusually lush or fast-growing grass above your drainage field
- the smell is worse after heavy rain or periods of high water use
- slow or blocked drains
- a gurgling or bubbling sound from indoor drains
This usually means your drainage field is struggling to absorb wastewater, or your tank is overloaded and needs emptying.
What to do next
A strong odour around your system may be a warning before it fails. Do not ignore it.
Call a specialist now. Acting quickly gives you the best chance of resolving the problem before it gets worse.
While you wait:
- reduce water use in your home immediately
- keep children and pets away from the drainage field area
- note when the smell is strongest and whether it's getting worse
Still not sure what's causing the smell?
Odours can be hard to diagnose without a proper inspection. If you're not sure what's causing the problem, we're here to help.
Tell us what you're noticing and we'll take it from there.
