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Why Does My Shower Drain Smell Bad?

November 23, 2016

That stench that’s ruining your showers has got to go. But in order to get rid of it, you need to determine what kind of smell it is.

First off, if your drain smells musty, you most likely have active mold growing underneath the drain cover. But if your drain smells like rotten eggs or sewage, you’re either smelling:

  • “Biofilm” from a clogged or dirty drain or
  • Sewer gases that have escaped your drainage pipes 

So, go back to your drain and take one last big whiff to identify which of the above problems is causing your drain to stink. Once you’ve identified the smell, skip to that section below for advice on how to get rid of that stink for good.

Not interested in DIY advice? Just contact us and we’ll send a plumber over immediately to get rid of that stench.

If your drain smells musty…

...you’re most likely smelling mold that’s growing in your drain. 

As part of their metabolic process, active mold spores release tiny puffs of gas that have a distinct musty smell. What’s worse is that gas can be dangerous. If inhaled, it can cause headaches, nausea, dizziness and fatigue.

So, how do you get rid of those active mold colonies? Well, according to the EPA, if the mold infected area is less than 10 square feet, you should be able to handle the cleanup yourself. Just follow the steps below.

What you’ll need:

  • Baking soda
  • White distilled vinegar
  • Boiling water
  • Old toothbrush

Steps to remove mold from shower drain:

  1. Mix equal parts baking soda and water to create a paste.
  2. Use the toothbrush to apply the paste over the shower drain.
  3. Wait 10 minutes. Then use the toothbrush to scrub the entire shower drain thoroughly. Repeat as many times as needed to loosen any mold around or under the shower drain.
  4. Boil 10 quarts of water, wait for it to cool and pour it slowly down the drain. Tip: If you have PVC piping, boiling water (212 degrees F) can damage it. Water that is approximately 140-150 degrees should be hot enough to kill mold.
  5. Pour a cup of vinegar down the drain slowly.
  6. Pour a half cup of baking soda down the drain.

If your drain still smells like mildew after this or if the smell disappears then returns, you may have a larger mold problem that requires professional cleaning. 

Word to the wise: There is a high possibility that black mold will reappear even after professional drain cleaning. That’s because mold needs food, moisture and warm temperatures to thrive, all of which are offered inside your shower drain. Ask your plumber for professional prevention techniques to keep the mold away.

If your drain smells like rotten eggs or sewage…

...you have one of 2 issues:

  1. Biofilm from a clogged drain 
  2. Sewer gases are escaping your pipes

Let’s take a look at both problems.

Problem #1: Biofilm from a clogged or dirty drain

First off, run your shower water for 2-5 minutes. Do you have a slow drain? 

If so, that smell is the buildup of bacteria and decomposing debris inside your drain called “biofilm.” And that bacteria emits a sticky, glue-like substance that allows them to stick to almost any surface. Gross, right? 

To get rid of that smell, you’ll want to get rid of the clog and debris that is trapping (and feeding) all that bacteria. Follow the steps below to do just that.

Don’t have a slow drain? Skip the the sewer gases section below.

What you’ll need:

Steps to clear a clog in your shower drain:

  1. Remove the shower drain with the screwdriver. You may have a push-pull drain, in which case you can unscrew the drain by turning it counter-clockwise.
  2. Boil 5 to 10 quarts of water and let it cool to 150 degrees F. Then pour it slowly down the drain.
  3. Pour one cup of vinegar down the drain.
  4. Pour a half cup of baking soda immediately after the vinegar.
  5. Wait 2 hours then pour a gallon of hot water down the drain.
  6. Run a drain brush down the drain to remove any leftover debris. This also helps loosen and remove the biofilm’s sticky residue.

If you still have a clog after this, you’ll need to have a professional clear your drain.

Problem #2: Sewer gases are escaping your pipes

If you don’t have a slow drain, you most likely are smelling sewer gases, also known as hydrogen sulfide

Don’t worry, the amount you’re breathing in isn’t dangerous to your health. But the smell does indicate that you have problems somewhere in your drainage system. You see, your drain pipes are designed to prevent any hydrogen sulfide from wafting back into your home.

The problems you could have include:

  • A dry P-trap
  • No P-trap
  • Sewer backup

Unfortunately, you can only solve the first problem on your own. The others you’ll need a professional to fix. But before you call your plumber, try the following steps to see if your problem is just a dry P-trap!

How to fix a dry P-trap:
First, shine a flashlight down your shower drain. Do you see water at the bottom of the pipe connected to the drain?

If so, you don’t have a dry P-trap and will need a professional to inspect your drainage system for other problems. 

But if you don’t see water, you most likely have a dry P-trap. Don’t worry, we’ll show you how to fix that. But first, what’s a P-trap and why is it bad if it’s “dry”?

A P-trap is a U-shaped pipe that attaches to every drain in your home. It’s designed to trap a small amount of water that blocks sewer gases from wafting back into your home.

The P-trap (the black curved pipe) contains a layer of water that acts as a seal. That seal blocks sewer gases from seaping into your home.

But, sometimes, those P-traps can dry out and leak nasty smelling sewer gases into your home. Thankfully, there’s an easy fix. 

Follow these steps to fix a dry P-trap:

  1. Pour one or two cups of water down the drain and wait an hour.
  2. After an hour, take a look down the drain to make sure you can still see the water.
  3. If the shower barely gets used, pour 4 ounces of mineral or cooking oil down the drain. (This slows evaporation and will keep the water in the trap longer.)

Note: If your P-trap becomes dry soon after this, you most likely have a cracked or broken P-trap and you’ll need to have a professional repair or replace it.

Need a plumber to get rid of that smell?

If you live in the Denver or surrounding area, we’re here to help. Just schedule your appointment today and we’ll send over an experienced plumber to fix the problem.

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