Persistent sewer odor in my basement driving me crazy

[ybnewhomeowner]

Hi guys,

I live in a 1970s townhouse in BC, Canada and have been experiencing a persistent sewer odor in my basement. It is driving me mad. I have identified the floor drain as one confirmed source of the odor, but there could be other additional sources. Below are some details

1. Floor drain (confirmed source of sewer odor)
This is the picture: I have poured (big) buckets of water into the drain, have scrubbed the inside of the drain using a toilet brush with toilet cleaner and bleach, and used the baking soda/vinegar cleaning method. No difference. There does not seem to be any cloggagge in the drain, as water drains easily after being poured into the drain. Also, this floor drain does not appear to have a cleanout set up because I have not been able to see a clean out opening in the drain. It is not clear whether this floor drain is connected to the sewer system of the house.

2. Main sewer pipe (suspected,additional source of sewer odor)
This is the picture of the main sewer pipe:
Intermittently, when I get closer to sewer main and bend down, the sewer odor grows stronger, so it could also be a source of sewer gas. The cleanout plug used to leak, but I replaced it with a new one, and it does not clean leak any more.

3. Added drainage line (suspected. additional source of sewer odor)
Please see this picture:
It appears that the previous owner of this house added a line that would drain into the main sewer pipe. It possibly could have been for an appliance such as a dehumidifier. That line is not being used, but not properly sealed. As a temporary measure, I have used tape to seal the cut plastic tubing, and also the barb. Not sure how effective it is, but when I get closer, I do not detect any stronger sewer odor.

Any suggestions and thoughts? How can I get the floor drain to stop producing the horrible smell? Thanks! I am getting really desperate.

 

[Twowaxhack]

Seal the floor drain off with tape and see if the smell goes away.

 

[ybnewhomeowner]

Seal the floor drain off with tape and see if the smell goes away.

Thanks for your reply. I did do that already, which is why you see all the peeled off paint around the edge of the drain. It appears that the smell did go away (or was at least substantially reduced) for a couple of days, but then it came back. Now, there could be a number of reasons. The first is that I was not able to completely seal it off with tape because the floor was rough and uneven. I just used regular packing tape. Is there any special type of tape for sealing off drains? The second possible reason is that there are other sources of odor (e.g. the sewer main line).

 

[Twowaxhack]

You could buy a test plug and seal the drain off with that. Home Depot and Lowes sells them.

You could also get some plastic bags and put a wash cloth in the bags and shove that in the drain real tight.

Once the smell completely goes away for 3-4 days, remove the bag or test plug and see if the smell comes back.

 

[ybnewhomeowner]

You could buy a test plug and seal the drain off with that. Home Depot and Lowes sells them.

You could also get some plastic bags and put a wash cloth in the bags and shove that in the drain real tight.

Once the smell completely goes away for 3-4 days, remove the bag or test plug and see if the smell comes back.

Thank you for providing the name of that plug I have been looking for. I had been searching under the term twist plug, but could not find what I was looking for.

Now, assuming that the smell is completely gone, and then comes back when the plug is removed, what does that tell me? There is still the question of how to make the drain functional without being god awful smelly.

 

[Twowaxhack]

The test will show us the way. Let us not worry.

 

[CT18]

Is the P trap for the floor drain holding water. I had a P trap that was split and wouldn't hold water.

 

[MicEd69]

It's hard to tell from the picture, but can you see water standing in the drain line? You should be able to see the water. Like CT18 said, if there is no water in the trap, there is no seal to prevent sewer gases from coming up through the drain.

 

[Twowaxhack]

I can see water in the trap in the picture.

 

[pasadena_commut]

The OP could buy a natural gas leak detector, the kind that gives a (semi) quantitative reading of all types of combustible, and use that to map the local methane concentration. Just walk around slowly, possibly very slowly, taking readings until the highest concentrations are found. This should work because typically there is methane in sewer gases. At least it should if the device is sensitive enough. There are a ton of these for sale on Amazon. As is typical with devices from there, evidence that they actually work is mostly anecdotal. This one has high sales numbers, good reviews, adjustable sensitivity, and it is cheap:

https://www.amazon.com/Natural-Detector-Portable-Combustible-Explosive/dp/B07FSVCSSL/

(I have no personal knowledge if this particular device works. It does mention "sewer gas" as being one of the things it detects.)

Is there any chance that there is a sewer leak under the building? Gases from that could come up through the soil and enter the basement through cracks in the floor, or any other opening, like where where a pipe goes through the concrete.

 

[pasadena_commut]

Revisiting the "sealing the floor drain" issue. I would obtain a plate of transparent impermeable material, like a 1/4" or 3/8" sheet of plastic, that was at least a couple of inches wider than that hole. Clean the floor thoroughly (no dirt, no loose paint). Get some plumber's putty and put a ribbon all the way around the drain and maybe 1" out, let's say 1/2" thick. You don't want putty going into the drain. Put the plate on, then press down on it evenly, or slowly add weights, to compress the putty. Then remove the weight and check that the putty is spread well and doesn't have any channels through it. That should hold in any sewer gas. Put the weight back on (so any gas pressure doesn't break the seal). Air out the basement to the extent possible (use an exhaust fan if available). See how long that keeps the smell at bay. If it comes back, sniff around the sealed drain, then elsewhere.

After the experiment stick a knife in under the plate to break the seal, Then work around cutting the putty. It could also be cut by sawing underneath with a wire. Most of it should come off the floor with a plastic putty knife, and then scrub the rest off.

Silicone would probably seal better, but getting the plate back off would be much harder.

 

[three_jeeps]

Since you said the smell seems to be intermittent, that suggests to me that perhaps there is some down stream condition that would cause sewer gas to 'bubble up' intermittently through the line. Water in the trap *should* provide enough of a static head pressure to block the gas. Perhaps getting a web cam (e.g. Wyze Cam), put it around the drain and have it trigger on any motion might help isolate the problem.
I am not familiar with how sewer lines are laid out so it is possible that this condition would never exist. If so, just ignore this suggestion.

 

[Twowaxhack]

Since you said the smell seems to be intermittent, that suggests to me that perhaps there is some down stream condition that would cause sewer gas to 'bubble up' intermittently through the line. Water in the trap *should* provide enough of a static head pressure to block the gas. Perhaps getting a web cam (e.g. Wyze Cam), put it around the drain and have it trigger on any motion might help isolate the problem.
I am not familiar with how sewer lines are laid out so it is possible that this condition would never exist. If so, just ignore this suggestion.

That’s possible.

 

[Twowaxhack]

Revisiting the "sealing the floor drain" issue. I would obtain a plate of transparent impermeable material, like a 1/4" or 3/8" sheet of plastic, that was at least a couple of inches wider than that hole. Clean the floor thoroughly (no dirt, no loose paint). Get some plumber's putty and put a ribbon all the way around the drain and maybe 1" out, let's say 1/2" thick. You don't want putty going into the drain. Put the plate on, then press down on it evenly, or slowly add weights, to compress the putty. Then remove the weight and check that the putty is spread well and doesn't have any channels through it. That should hold in any sewer gas. Put the weight back on (so any gas pressure doesn't break the seal). Air out the basement to the extent possible (use an exhaust fan if available). See how long that keeps the smell at bay. If it comes back, sniff around the sealed drain, then elsewhere.

After the experiment stick a knife in under the plate to break the seal, Then work around cutting the putty. It could also be cut by sawing underneath with a wire. Most of it should come off the floor with a plastic putty knife, and then scrub the rest off.

Silicone would probably seal better, but getting the plate back off would be much harder.

All that’s not necessary. A plastic bag with a wash cloth stuffed in the hole works fine.

When I do remodels that’s what we do and there are never complaints of sewer gas. And believe me when you charge $200-300 an hour people aren’t shy to complain.

Let’s not make this any harder than it is because it’s pretty simple.

 

[ybnewhomeowner]

Is the P trap for the floor drain holding water. I had a P trap that was split and wouldn't hold water.

Hi, yes, there is standing water in the drain. And water in the drain remained at the same level after buckets of water were dumped into the drain. I guess that means the p-trap is intact? I am just a new home owner, not a plumber.

 

[pasadena_commut]

... would cause sewer gas to 'bubble up' intermittently through the line.

If a house's sewer line is partially blocked and the tub is run or one toilet flushes it can cause bubbles in another toilet. The rising water and air in the line pushes some of the air out of the trap. I suppose that might be possible here if there is a partial blockage downstream of where the OP's sewer line goes into the main. That said, I have had the displeasure of personally observing the symptoms of a main sewer line blockage, and it wasn't just bubbles coming out. If that was what was going on the water level in that trap would rise, and unless it was "just so", water (and worse) would pour out onto the floor.

Still, a testable hypothesis. If the OP runs a lot of water elsewhere in the house, and watches that drain, it should eventually bubble and then back up if there is an issue like that. It could take quite a lot of water though to get to that point, possibly more than his one house can supply.

 

[ybnewhomeowner]

The OP could buy a natural gas leak detector, the kind that gives a (semi) quantitative reading of all types of combustible, and use that to map the local methane concentration. Just walk around slowly, possibly very slowly, taking readings until the highest concentrations are found. This should work because typically there is methane in sewer gases. At least it should if the device is sensitive enough. There are a ton of these for sale on Amazon. As is typical with devices from there, evidence that they actually work is mostly anecdotal. This one has high sales numbers, good reviews, adjustable sensitivity, and it is cheap:

(I have no personal knowledge if this particular device works. It does mention "sewer gas" as being one of the things it detects.)

Is there any chance that there is a sewer leak under the building? Gases from that could come up through the soil and enter the basement through cracks in the floor, or any other opening, like where where a pipe goes through the concrete.

Thanks! I think I will get one such detector.

You asked whether there is a chance there is a sewer leak under the building. That's one of the worst scenarios I have in my mind, as this would be very expensive to fix, I would imagine. I don't really know! Would there be signs other than odor in the basement that would indicate such a problem?

 

[ybnewhomeowner]

Revisiting the "sealing the floor drain" issue. I would obtain a plate of transparent impermeable material, like a 1/4" or 3/8" sheet of plastic, that was at least a couple of inches wider than that hole. Clean the floor thoroughly (no dirt, no loose paint). Get some plumber's putty and put a ribbon all the way around the drain and maybe 1" out, let's say 1/2" thick. You don't want putty going into the drain. Put the plate on, then press down on it evenly, or slowly add weights, to compress the putty. Then remove the weight and check that the putty is spread well and doesn't have any channels through it. That should hold in any sewer gas. Put the weight back on (so any gas pressure doesn't break the seal). Air out the basement to the extent possible (use an exhaust fan if available). See how long that keeps the smell at bay. If it comes back, sniff around the sealed drain, then elsewhere.

After the experiment stick a knife in under the plate to break the seal, Then work around cutting the putty. It could also be cut by sawing underneath with a wire. Most of it should come off the floor with a plastic putty knife, and then scrub the rest off.

Silicone would probably seal better, but getting the plate back off would be much harder.

So I went to get both a test plug (suggested by another commenter), and plumber's putty. Now, what kind of "sheet of plastic" were you suggesting? Is it a specific type used for plumbing jobs? Can I cut out a side of a jumbo ziploc bag and use that?

 

[pasadena_commut]

Definitely not something normally used in plumbing - like a pane of glass, but transparent plastic. Acrylic (AKA plexiglass) or polycarbonate (Lexan) or something like that. Don't use real glass, it might crack or shatter. The idea is to seal over the drain but still be able to see into it so that you can spot any defects in the putty seal. Home Depot (if you have that in Canada) sells a small thin sheet which would probably work. Otherwise, dedicated plastic stores (like TAP plastics) carry them, as do places that make custom picture frames and some hobby stores.

Plastics are pretty much all somewhat gas permeable for small molecules. However, for anything more than a thin film the rate at which these molecules get through is small. So gas masks and respirators for serious chemical work can use polycarbonate visors. For this application I would guess that 1 mm or more thick should be enough.

Plumber's putty isn't supposed to be used on plastics, but it should be fine for a week or two. Over more extended periods the oil in the putty will degrade the plastic.

If you don't care about the transparency a flat piece of metal you might have around the house would work. Metal isn't usually gas permeable (except for hydrogen). Don't use aluminum foil though, it is common for it to have or develop holes . Home Depot sells some aluminum sheets for roofing repairs which would make a good seal and they are not very expensive. Just don't let it contact a different metal in that wet/humid environment.

 

[Twowaxhack]

Lord have mercy