Why is there a sewage smell in your bathroom?

Why is there a sewage smell in my bathroom?
It's not uncommon for your bathroom to occasionally have bad odors, but if you smell sewage, that's not a good sign. DigitalVision/Getty Images

You walk into your bathroom and crinkle your nose as you detect the faint smell of sewage coming from ... somewhere. While most bathrooms are occasionally home to unfortunate odors, this one is distinctly out of place.

You lean closer to the sink, the shower drain and the toilet as you try to identify the source of the offensive odor. You squeeze some cleaner into the toilet bowl and give it an extra scrub, even though it has been recently sanitized. With that, the fragrance of the cleaner temporarily masks the smell, and you leave the room. Later, you catch another whiff as you walk past the bathroom door. This time, the smell is unmistakable, and no amount of scrubbing, running the fan or spraying air freshener is able to resolve it. So why is there a sewage smell in your bathroom?

The bad news is that any number of things can cause a sewage smell in your bathroom, and it can be difficult to pinpoint the source of the odor. Besides the obvious unpleasant smell, the methane in sewer gas can actually be flammable in large quantities, and breathing it in can be hazardous to your health. Fortunately, once the source of the problem is identified, the sewage smell is usually pretty simple and inexpensive to correct. Want your clean-smelling bathroom back? Read on!

Plumbing 101

To figure out what might be causing that awful smell, it helps to have a basic understanding of how your bathroom plumbing works.
To figure out what might be causing that awful smell, it helps to have a basic understanding of how your bathroom plumbing works.

To figure out what might be causing that awful smell, it helps to have a basic understanding of how the plumbing in your bathroom works. (Don't worry -- this will be quick!)

At some point, you've probably looked under the bathroom sink and noticed the U-shaped pipe that runs from your sink drain (B) to a larger wastewater pipe in the wall. This pipe is called the P-trap. One end of the P-trap runs down to your sewer or septic system (E); the other end leads all the way up through the roof (D), letting fresh air in while allowing any smelly sewer gases to vent out to the sky. And although you can't see it, the same basic drain setup is at work behind or beneath your tub and shower (C).

The U-shape of the P-trap allows it to collect a small amount of water after each sink use, which acts as a barrier against sewage odors. When everything's working as it should, the water stays in the P-trap after you turn off the sink, empty the tub or flush the toilet. That little bit of water is enough to prevent gases from drifting out of the sewage system and into your house. Under normal conditions, those gases flow right past your bathroom and out through the vent pipe in your roof [source: Wm. Henderson].

"The role of the P-Trap is to keep the sewer gases out of the home," says Ray Patrick, a master plumber with Roto-Rooter. "There are misconceptions that the traps are also there to catch objects that might be dropped in the drain, which is not the case. Traps are there to prevent sewer gases from escaping into the home."

Failure to properly vent those stinky gases has the potential to be more than just annoying. "It could be dangerous because of other gases that can be present in sewer systems. Methane is the largest cause of sewer smell but there is also danger of hydrogen sulfide, carbon dioxide, ammonia, nitrogen oxides and sulfur dioxide," explains Patrick in an email interview, adding that the main culprit of such added toxins are people disposing of gasoline and other chemicals down their drains. Signs of exposure can include dizziness, headaches, nausea and drowsiness.

Clearly, it's important to figure out exactly what's causing the sewage smell and make sure it's corrected quickly and effectively. If you're lucky, it will be one of the easy fixes on the next page.

Easy Fixes for that Sewage Smell

The first possible cause of a sewage smell in your bathroom is by far the easiest to fix, and more likely to occur in bathrooms where fixtures haven't been used recently, such as the sink in a guest bathroom or the tub in a bathroom with a separate shower. The issue in situations like these is that the water in the P-trap has simply evaporated due to lack of use, effectively removing the barrier between your bathroom and the gases in the sewer system. If that's the case, the solution is as simple as running some water to allow the P-trap to fill up again [source: Wm. Henderson]. If plain running water isn't cutting it, Patrick recommends using pink RV water-safe antifreeze.

If there's still a sewage odor after you've run plenty of water or pink antifreeze down all the drains, or if you notice a sewage smell in a bathroom that gets regular use, you might want to check for leaks in or around the P-trap. If even a small amount of water has leaked out of the bottom of the "U," sewage gases may be able to sneak in. "If anything leaks, it would be noticeable," Patrick explains.

Another possible cause that's kind of gross, but fairly easy to resolve is a clog in the drain, since the clog itself can become smelly. Often, a plunger can take care of the clog, but if that doesn't work a plumber might have to use a drain snake or hydro-jetter to remove it. Sometimes, it's necessary to completely remove the P-trap to solve the issue [source: Wm. Henderson].

If the suggestions above don't lead you to the source of the sewage smell, you may be dealing with a more complicated issue. Keep reading to troubleshoot this troublesome issue.

Time to Call the Plumber!

Time to Call the Plumber!
Sometimes you can fix the problem yourself but other times you need to call a plumber. Perry Gerenday/Getty Images

So, there's water in all the P-traps, you have no visible leaks and the pipes are free of clogs. What next?

It seems natural to assume that the toilet would be the obvious source of any sewage smells, but if there's water in the bowl, chances are the commode is not the problem. This is because the toilet water acts as a smell barrier -- just like the water in a sink's P-trap. But if the bowl doesn't fill up as it should, the problem could be a broken seal. When there is no caulk around the base of the toilet, water and urine can seep underneath and water that gets stuck in crevices and doesn't dry will grow bacteria. This bacterium can often cause a foul odor if left unchecked [source: Angie's List]. This is an issue that Patrick encounters frequently, noting that that it's easy enough to solve by adding a bead of caulk around the bottom. Sometimes it's also necessary to caulk the bolt holes because smell can leak through there, too, he says.

The wax ring, which is installed with a toilet to seal the drain and prevent water seepage, can be damaged if the toilet bowl is loose. This can result in water leaks and sewage smell. So, you should check to see if your toilet bowl is loose or wobbly – if it is, you can reset the toilet with a new toilet ring [source: Angie's List].

Occasionally, the problem is actually coming from somewhere else, even though the smell itself is inside the bathroom. For example, a roof vent blocked by a bird's nest, leaves, or snow and ice prevents fresh air from coming into the plumbing system and preventing the sewage system from venting the way it's supposed to. It can be tricky to distinguish between a blocked drain pipe and a blocked vent, so homeowners often spend plenty of time focusing their efforts on a single pipe. A few telltale signs (in addition to the sewage smell) that a blocked vent is actually the culprit are that all of the drains in the home are slow to drain, and that water makes gurgling noises or bubbles up when trying to drain [source: Jim Dhamer Plumbing and Sewer, Inc.].

A vent pipe that's been improperly installed, cut or cracked can also send offensive gases into your home. A cracked vent pipe can be even harder to track down, since the break is probably hidden somewhere within your walls. Fortunately, a plumber can locate a vent pipe leak with a device called a smoke machine, which fills the drain system with a harmless visible smoke. When the smoke finds its way out, the source of the leak is obvious [source: American Leak Detection].

Although some of the fixes are done easily enough by the average homeowner, you should evaluate your comfort and skill level before tackling a project like this. If you're handy, you could take care of cleaning drains or perhaps replacing a toilet's wax ring. But if you're not comfortable doing home repairs, or you're not sure of where the smell is coming from, it might be best to hire a pro.

Last editorial update on Apr 23, 2018 02:03:46 pm.

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Sources

  • American Leak Detection. "Smoke Testing for Leak Detection." 2018 (April 19, 2018) https://www.americanleakdetection.com/residential/plumbing/smoke-testing/
  • Angie's List, with PR Dept. Email interview, April 19, 2018.
  • Angie's List. "Sewers and Main Drains." 2018 (April 19, 2018) https://www.angieslist.com/research/sewer-and-main-drains/
  • Carter, Tim. "Sewer Gas Smell." Ask the Builder. (June 8, 2012) http://www.askthebuilder.com/sewer-gas-smell/
  • Carter, Tim. "Sewer Odors in Bathroom." Ask the Builder. (June 8, 2012) http://www.askthebuilder.com/sewer-odors-in-bathroom/
  • Dhamer, Jim. "Blocked Sewer Vents: An Often Overlooked Plumbing Issue." Jim Dhamer Plumbing and Sewer, Inc. March 3, 2017 (April 19, 2018) https://dhamerplumbing.com/blocked-sewer-vents-often-overlooked-plumbing-issue/
  • Patrick, Ray. Master Plumber, Roto-Rooter Services Company. Email interview, April 18, 2018.
  • Plumbing Forum. "Sewer Smell in Bathroom Sink." Plbg.com. (June 8, 2012) http://www.plbg.com/forum/read.php?1,458709
  • Wm. Henderson. "Plumbing Repair Question: What Does the U-shaped Pipe Under a Sink Do?" March 19, 2014 (April 19, 2018) http://www.wmhendersoninc.com/blog/plumbing-service/plumbing-repair-question-what-is-the-u-shaped-pipe-under-a-sink-do/