Phew! That awful smell! Is sewer gas invading your home through the shower drain?

©Copyright by Jaye Denman. All rights reserved.

If you smell a noxious sewer-like odor inside your home, chances are it is sewer gas escaping from the drainage system. Sewer gas not only smells gross, the methane and bacteria it contains can be dangerous to your health, causing headaches or even more serious ailments. Even scarier, high concentrations of methane gas are combustible, which can cause an explosion. If you notice this distinctive foul odor, it should not be ignored.

Before you call the plumber, however, there are some simple DIY actions that may eliminate the problem quickly and at little or no cost.

Plumbing fixtures and their connecting systems that are correctly designed and installed are normally odorless. However, even the best plumbing may sometimes allow sewer gas into your home due to a simple problem that can be easily checked…and simply solved. If the problem persists, then it’s time to call in the professional—a plumber.

How does sewer gas get inside your home?

Every drain in your home’s sewer system should have a “p”-shaped trap that is properly vented. These drains “trap” water, creating a seal, or barrier, that will keep sewer gas out of your home. If one of these drains is rarely used, such as in a guest bathroom, the water creating the protective seal will eventually evaporate. This is a formula for trouble that can allow stinky sewer gas to seep into your home.

I didn’t know anything about p-traps or their function until a recent unpleasant incident forced me to do some hurried research. Here’s the background. There are three showers in my home. Two of them are used regularly. The third is rarely used at all. In fact, it had not been used for months at the time this situation occurred.

When that shower was suddenly used after remaining dry for such a long period, the resulting odor emanating from the shower drain after the water stopped was dreadful. It smelled like…yes, a sewer! Eau de sewer is definitely not the "fragrance" I wanted wafting throughout my home, so getting rid of it was top priority, requiring immediate action.

It was evening when the odor materialized, and I realized it might not be possible to get a licensed plumber to my house after regular business hours. Even if I were successful in locating a plumber who would show up before the next day, the overtime rates charged would not be healthy for my budget. Perhaps there was something I could do before then. DIY is not my forte, but I can sometimes handle an easy fix. You never know until you try.

The odor in the bathroom had to be contained, so closing off the drain holes temporarily was the first thing I did. I quickly dried the floor of the shower stall with paper towels and covered the drain tightly with good old all-purpose duct tape. I then opened the bathroom window for ventilation. Closing the door of that bathroom, I rolled up a towel and pushed it against the outside bottom of the door to prevent sewer gas from escaping that room into another part of the house.

Now that the odor was restricted, I headed for the computer and accessed Google. It took me only a few minutes to find several articles that explained how p-traps, vents (those pipes protruding from the top of the house) and a home’s plumbing drains are supposed to work, as well as what sometimes goes wrong to cause drain odors.

Let’s consider how the plumbing for this stand-alone shower in my home operates. Water from the city water system enters through the shower head, while faucets control the water pressure and supply. When water drains from the shower, it goes into the beginning of the city sewer system.

My shower, indeed every plumbing fixture in my home, should have two items working together to keep sewer gas out: (1) a p-trap that holds water in a “U” shape of the pipe and forms a seal, and (2) a vent system that allows air in to equalize pressure and lets sewer gases escape up the stack to the outside. In short, the properly-vented p-trap prevents back pressure from letting sewer gas into the house. The vent is a critical component of this system because the pressure in sewer lines may fluctuate.

I make a quick diagnosis

My research led me to believe that my current “stinky” problem might be the easiest type to resolve. Since the shower had remained unused for a long time, it very likely had a “dry trap.” There were several suggested remedies. Each of them used ordinary household products, such as baking soda, white vinegar, table salt, baking powder, hydrogen peroxide, chlorine bleach, boiling water. These were all items in my pantry, So far, so good.

This is the method I opted to use. I removed the duct tape and poured one cup of white vinegar into the drain, followed by one-fourth cup of baking soda, brushing the latter into the holes. I let that sit for two hours with the bathroom door closed. Then I slowly poured a gallon of hot (just-off-the-stove-boiling) water through the drain.

Next, I poured one-half cup chlorine bleach into the drain and let it sit for another two hours. This was followed by another gallon of boiling water poured slowly into the drain. I then turned on the shower’s hot water faucet, and let the water run for ten minutes. By then, ample water should be standing in the “U” curve of the p-trap. The last step was to pour four ounces of mineral oil (plain cooking oil will work in a pinch) into the drain. The oil floats on the water in the trap and slows evaporation. At that point, I was tired (it was very late by then), so I closed the door to that bathroom and got ready for bed.

When I got up the next morning, the first thing I did was check the “smell level” of the problem bathroom. No stinky odor. Success! No plumbing bill this time.

If the odor had persisted after the vinegar-baking soda-bleach-hot water-mineral oil technique I used that night, the sewer gas invasion might have been caused by something other than a dry p-trap. Leaks, rotted or cracked drain pipes, clogs in the drain or a stopped-up vent pipe are other potential “stink” makers. Had I still smelled that nasty odor when I opened the bathroom door next morning, stronger measures would have been in order. I was keenly aware I didn’t have the DIY expertise to test or resolve more difficult issues.

It would have been time to call in the professional—a licensed, bonded and insured plumber. I already have the phone numbers of two such plumbers on my speed dial (see next paragraph), but anyone searching for a plumber you can trust should use an Internet search engine for a national or local director of plumbers who are licensed, bonded and insured. You don't want to take a chance on someone who may charge cheaper rates, but can't be held accountable for work, including any damages to your property.

When I first bought this vintage ‘60s house eleven years ago, major plumbing problems seemed to crop up every few months. For quite some time, I had the phone number of my plumber of choice available to call quickly when emergencies arose. Finally, the big issues were resolved (and please don’t remind me how much money that cost), so visits from the plumber have been rare in recent years. (Knock on wood!) Still, I realize that letting a not-so-large problem go unrepaired often means it morphs into something much worse. All the years of plumbing problems gave me a healthy respect for those brave souls who successfully ply the trade. If a plumber is needed, at least I know a couple of good ones!

Since the sewer gas that invaded my home was only due to a dry trap, it's up to me to keep it from happening again. I now ensure there is a water barrier in the p-trap of that little-used shower with some easy weekly maintenance. First, I pour a cup of white vinegar down the drain, then turn on the water and let it run for about ten minutes.

If any plumbing fixture in your home gets infrequent use, try some "preventive maintenance" by running water or flushing to keep all the p-traps working properly. You won't be sorry for the effort if you keep nasty sewer gas at bay.

NOTE TO READERS: I will appreciate it very much if you vote and also give me feedback about this article in the Comments section. If you used these tips for getting rid of sewer gas in your shower drain, please let me know how ( or if?) they worked for you. I hope you found this information helpful.

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