Why does my dishwasher smell like sewer gas

You’ve just finished loading the dishwasher and pressed start, but instead of the sound of clean dishes being washed, a foul, sewer-like odor begins to creep out from under the counter, making you wonder if something is seriously wrong with your plumbing.

If you’re dealing with a sewer smell from your dishwasher, it’s not just unpleasant—it’s a sign that something isn’t working right. The good news is that in most cases, the fix is simple and doesn’t require a plumber.

TL;DR
A sewer gas smell from your dishwasher is usually caused by trapped food particles in the filter that are decomposing, a clogged or incorrectly installed drain hose, or a missing high loop that allows dirty water to flow back into the machine. Start by cleaning the dishwasher filter thoroughly. Next, check that the drain hose is routed with a high loop under the sink to prevent backflow. If the smell persists, the drain hose or plumbing vent may be clogged and need professional attention.

Key Takeaways

Clean the Filter First: The most common cause of a sewer smell is food debris trapped in the dishwasher filter that has started to rot and smell like sewage .
Check the Drain Hose Installation: A missing or incorrectly installed high loop or air gap can allow dirty sink water to flow back into the dishwasher, causing that sewer odor .
Run a Cleaning Cycle: A hot cycle with a dishwasher cleaner or white vinegar can help remove grease, soap scum, and bacteria buildup that contribute to odors .
Inspect for Clogs: A blockage in the drain hose or sink trap can cause water to back up and smell .

Table of Contents

The Real Causes of That Sewer Smell (And How to Fix Them)

Dishwashers are a perfect environment for bacteria—they’re warm, wet, and constantly exposed to food particles. When the system isn’t draining properly or isn’t cleaned regularly, that combination creates a distinct sewer-like stench.

Dirty or Clogged Filter

This is the number one culprit. Your dishwasher has a filter designed to catch large food particles and prevent them from entering the drain. Over time, food debris builds up in the filter and on the surrounding parts, decomposing and creating a rotten, sewage-like odor .

“Most of the time, that nasty smell is coming from the dirty water stuck inside your dishwasher. The usual culprits are a clogged drain hose, drain, or filter. When food particles get trapped in the filter, the water can’t drain properly, and after sitting there for a while, it starts to smell” .

Incorrect Drain Hose Installation

If your filter is clean and the smell persists, the problem is likely in how the dishwasher drains. The drain hose must be installed with a “high loop”—an upward bend that rises as high as possible under the countertop before sloping down to the drain connection .

Without this high loop, dirty water from your kitchen sink or garbage disposal can flow backward into the dishwasher through the drain hose. This backflow brings food scraps and bacteria into the machine, creating a sewer smell .

If you have a garbage disposal, make sure the knockout plug was removed from the disposal inlet when the dishwasher was installed. Forgetting to remove it will prevent drainage entirely, leaving standing water in the machine that quickly smells like sewage .

Clogged Drain Hose or Plumbing Vent

A blockage in the drain hose itself can also cause smells. Food debris and grease can build up inside the hose, trapping water and bacteria . A kinked or damaged hose can restrict drainage and create the same problem .

In some cases, the issue is deeper in your plumbing. A clogged roof vent can create back-pressure in the pipes. When you try to drain water, the pressure forces sewer gas back into your kitchen through the dishwasher instead of venting outside .

Your Step-by-Step Fix Guide

Follow these steps in order. You’ll likely solve the problem before you reach the end.

Step 1: Clean the Dishwasher Filter

Locate the filter at the bottom of the dishwasher tub. It’s usually a cylindrical or flat piece that twists or pulls out .
Remove it and scrub away all the food particles and gunk using a brush and warm, soapy water .
Rinse it thoroughly and replace it. Do this at least once a month to prevent odors .

Step 2: Run a Deep Cleaning Cycle

After cleaning the filter, the interior needs a deep clean.

Place a dishwasher-safe bowl filled with white vinegar on the top rack.
Run the dishwasher on the hottest, longest cycle with no dishes and no detergent .
After that cycle finishes, sprinkle a cup of baking soda across the bottom of the dishwasher and run a short, hot rinse cycle. The vinegar and baking soda work together to break down grease and neutralize odors .

Step 3: Check the Drain Hose and Installation

If the smell is still there, it’s time to look under the sink.

Look for the High Loop: The dishwasher drain hose should rise to the highest point under the sink and be secured with a clamp before sloping down to the drain connection . The minimum height should be around 32 inches above the floor . If it’s just lying flat, that’s your problem.
Check for Kinks or Damage: Make sure the hose isn’t pinched, kinked, or cracked .
Knockout Plug: If your dishwasher drains into a garbage disposal, confirm the knockout plug was removed from the disposal inlet .
Clear the Hose: If you’re comfortable, place a container under the hose connections, detach the hose, and use a drain snake to clear out any trapped debris . If the hose is damaged, replace it—it’s an inexpensive DIY fix .

Step 4: When to Call a Plumber

Call a professional if:

The smell returns quickly after a thorough cleaning.
You suspect the problem is a clogged roof vent .
You find that the water is draining directly into the sewer side of the P-trap, not the sink side .
You’re not comfortable working under the sink or diagnosing plumbing issues .

Expert Insight: “If you’ve cleaned the filter and are still having bad dishwasher smells then you may have an issue with your vent or drain pipe” .

Frequently Asked Questions

Why does my dishwasher smell like sewage when it’s running?
This is usually caused by food particles trapped in the filter, or dirty water flowing back into the dishwasher due to a missing high loop or incorrectly installed drain hose .

Can a dirty garbage disposal cause my dishwasher to smell?
Yes. If your dishwasher drains into the same pipe as your disposal, a clogged or dirty disposal can force smelly water back into the dishwasher .

How often should I clean my dishwasher filter?
You should clean it at least once a month to prevent food buildup and odors . Some homeowners prefer to do it more often.

What is a dishwasher high loop, and why does it matter?
A high loop is a section of the drain hose that is routed up as high as possible under the countertop. It prevents dirty sink water from siphoning back into the dishwasher, which is a common cause of sewer smells .

How do I clean a smelly dishwasher naturally?
Run an empty hot cycle with a bowl of white vinegar on the top rack. After it finishes, sprinkle baking soda on the floor and run another hot rinse cycle .

What does a clogged dishwasher drain hose look like?
You might notice standing water in the bottom of the dishwasher after a cycle, slow drainage, or the smell of sewage . A small amount of water in the bottom is normal, but significant puddles point to a drain problem .

Which kitchen problem do you want solved next? Share your thoughts in the comments.

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Why Does My Dishwasher Smell Like Sewer Gas?