Introduction: The Smell That Wouldn’t Go Away

I never thought I’d need to Google, “why does my bathroom smell like sewage?”, but when that unmistakable sewer-like odour started creeping through my en-suite, I knew something wasn’t right.

At first, I ignored it, thinking it would go away. But it only got worse—especially after showers, at night, and when it rained. Eventually, I realised I needed answers—and fast.

So, I set out to understand why my bathroom smells like sewage, and more importantly, how to stop it using smart DIY ideas.

Why Does My Bathroom Smell Like Sewage? – Common Causes I Found

Before jumping into fixes, I wanted to get to the root of the smell. Here’s what I uncovered through research and hands-on inspection:

1. The Trap Seal Was Dry (Even When Nothing Leaked)

If your bathroom smells like sewage but there are no leaks, chances are the P-trap has dried out.

This happens when fixtures (like a guest bathroom shower) aren’t used regularly. The water barrier that blocks sewer gases simply evaporates.

2. Blocked or Dirty Drains

Sometimes the smell only appears after I shower—and that’s because hair, soap scum, and grime clog the drains over time.

This blockage creates the perfect environment for bad bacteria and gases to fester.

3. Cracked or Loose Seals That Aren’t Easy to Spot

I had no visible leaks, but a faint smell led me to inspect the toilet base—turns out the wax ring had cracked. Even a small seal break can let gases escape.

4. Ventilation Issues (Especially at Night or in Cold Weather)

Ever wonder why your bathroom smells like sewage at night or when it gets cold? I did too. Cold air increases pressure in your drainage system, pushing odours back inside.

Also, your bathroom vent pipe may be blocked or your extractor fan might be underperforming.

5. Sewer Line Pressure from Rainfall

Heavy rains can overload sewer systems.

I noticed the smell was strongest when it rained—that’s because the main sewer line was pushing gases back through the vent stack.

How Do I Stop My Bathroom from Smelling Like Sewer? – 5 Smart DIY Solutions

Once I knew the causes, I took action. Here are the 5 smart DIY solutions that worked for me:

1. Refill the P-Trap in Unused Fixtures

Sometimes, it’s just a simple case of evaporation.

How I fixed it?

• Ran water in toilets and all unused sinks and showers
  
• Poured a tablespoon of mineral oil to slow evaporation
  

Solved the issue when the smell occurred only sometimes or overnight

2. Clean Drains Naturally With Baking Soda and Vinegar

I avoided harsh chemicals and used this eco-friendly method:

Steps I followed:

• ½ cup of baking soda into the drain
  
• 1 cup of vinegar followed by covering the drain
  
• Waited 10–15 minutes and flushed with hot water
  

Best fix when the smell occurred after I showered

3. Snake the Drains and Use a Plunger

DIY Drain Unclogging:

• Used a drain snake to pull out hair and gunk
  
• Plunged the toilet and sink just in case of hidden blockage
  

Solved when the smell was strong with no visible leaks

4. Replace Toilet Wax Ring and Inspect Pipe Joints

A cracked wax ring may be invisible—but very smelly.

What I did?

• Removed the toilet
  
• Installed a new wax ring (under £10)
  
• Sealed joints with silicone for added security
  

Solved persistent odours with no obvious water leaks

5. Upgrade Ventilation to Prevent Odour Build-up

If your bathroom smells worse at night or in cold months, poor airflow is likely.

How I improved it?

• Installed a new extractor fan with humidity sensor
  
• Checked roof vent pipe for blockages using a torch
  

Prevented odours from returning after fixing the main issues

Quick DIY Checklist Before Calling a Professional

Before reaching for the phone, here’s what I personally checked:

• Refilled all trap seals
  
• Cleaned drains naturally
  
• Used drain snake and plunger
  
• Inspected toilet seal
  
• Upgraded extractor fan
  

Table: DIY vs When to Call a Plumber

Problem	DIY Fix	Call a Plumber If…
Trap seal dry	Refill with water	Smell returns after filling
Clogged drain	Baking soda, vinegar, snake	Multiple drains backing up
Toilet seal cracked	Replace wax ring	Toilet shifts or leaks water
Poor ventilation	New extractor fan, clear vent pipe	Walls show mould or fan fails to run properly
Foul smell during rain	Wait it out, flush drains	Sewage backs up into home

Why Does My Bathroom Smell Like Sewage Sometimes, Not Always?

I noticed that the smell came and went, especially during temperature shifts or when it rained.

That’s because sewer gas isn’t constantly being pushed into the bathroom—it builds pressure based on usage, air flow, and even weather.

Flushing all drains regularly and keeping traps wet helped me manage these “random” episodes.

Why Does My Bathroom Smell Like Sewage After Shower or At Night?

After shower: The hot water causes gases in the drain to expand and rise. Also, steam can push odours trapped in pipes into the air.

At night: Cooler air lowers pressure in the room but not in the pipes—this imbalance lets sewer gas rise through vent openings or cracked seals.

Why Does My Bathroom Smell Like Sewage When It Gets Cold or Rains?

Cold weather slows water flow, dries out traps, and worsens air pressure differences that lead to odours.

When it rains, external sewer lines can be overwhelmed, pushing back gases through vent pipes and drains.

Conclusion: What Finally Worked for Me

Dealing with a sewage smell in my bathroom felt overwhelming at first—but with a bit of patience and hands-on effort, I was able to fix it without calling a plumber.

The key was understanding the root cause, then applying smart, low-cost fixes. Now, my bathroom stays fresh all year round—no matter the weather, the time of day, or how often it’s used.

If your bathroom ever starts to smell like something died in the drains, don’t panic. Follow these steps on why does my bathroom smell like sewage, check the basics, and you’ll likely sort it out on your own—just like I did.