Sewer gas smell, completely stumped!

[Lucas Keppers]

So I've been in a house for about 1 1/2 years now and every once in a while I will get a sewer gas smell coming from one drain in my house. It happens at random but almost always at night and I've just about tried everything I can think of to fix it. I put a mechanical vent in front of it to prevent the trap from being sucked out and change the 2 other aav's I know of to a larger size. It has a 2" vent coming out of the roof and a 4" pipe to the sewer. I'm not sure how common it is for the system to become overpressurerized but it's not making any sense why it would be this one drain with the issue. I have tried to flush or drain everything in the house and it wont smell but at 1 in the morning I will wake up to the house being filled with sewer gas. I've even went into the crawlspace underneath the drain when it is smelling and I dont hear or smell anything down there. I will turn on the washer and let it run a cycle to no avail in stopping the gas from entering. I currently have a rubber ring in the drain that somewhat seals around the hose but it still pushes through that as well. I have also made sure that the hose is not down past the p-trap. The only option I can think of at this point is to branch off another part of the plumbing upstairs and add another 2" vent that would run out of one of my eaves. But the part that has me so confused is why just the one drain that is the closest to my actual outside vent. I am currently hooked up to public sewer but there used to be a septic tank and there is a natural spring that runs buy that side of the house. Not sure if those could be contributing to the issue or not.

 

[Reach4]

So I've been in a house for about 1 1/2 years now and every once in a while I will get a sewer gas smell coming from one drain in my house.

Floor drain? Laundry tub? Laundry standpipe?

 

[Sponsor]

 

[Lucas Keppers]

Floor drain? Laundry tub? Laundry standpipe?

It's a laundry standpipe.

 

[Reach4]

Let's see a photo of the standpipe, its trap, and its vent line.

Is everything concealed in a wall?

 

[Lucas Keppers]

Let's see a photo of the standpipe, its trap, and its vent line.

Is everything concealed in a wall?

The AAV, standpipe and vent are concealed behind the wall but I do have a photo of the trap from the crawlspace. As far as the sewer layout goes I've drawn a diagram. The pipe for the vent to the roof is at the wrong grade and has the potential to back up. But every time I've been down there I've checked it for water and there is nothing. Additionally I will get the smell on days with no rain. The other day I hadn't had this issue for well over 2 months and then it just happened at 8 pm on a sunny day.

 

[Reach4]

Is there an AAV off to the left of the 20200223_174802.jpg photo?

A laundry standpipe trap is not allowed below the floor in the US, but it is in Canada.

How far do you think dimension max 42" is for you? That max is only 30 for UPC. The purpose of having a max is to prevent the trap from siphoning dry.

I had thought that most washing machines end up with just little dribbles a the end, and those would probably refill a siphoned trap. But maybe not, and your trap sometimes siphons.

 

[Lucas Keppers]

Is there an AAV off to the left of the 20200223_174802.jpg photo?

A laundry standpipe trap is not allowed below the floor in the US, but it is in Canada.

How far do you think dimension max 42" is for you? That max is only 30 for UPC. The purpose of having a max is to prevent the trap from siphoning dry.

I had thought that most washing machines end up with just little dribbles a the end, and those would probably refill a siphoned trap. But maybe not, and your trap sometimes siphons.

Yes the AAV is right after the edge of the photo. Its definitely more the 42", I would say more like 50"-56" to the p-trap. The only thing is the randomness of when this happens. If after a load of laundry I had the smell I would say this is the issue. But agian it sometimes when the washer hasn't been run for hours or the day. It will generally last 30 minutes to 2 hours and will allow gas through the pipe even if I hand pour water or run the washer. I do have a very long drain hose for the washer, would it compensate for the issue if I dropped it down to right above the p-trap?

 

[Reach4]

I do have a very long drain hose for the washer, would it compensate for the issue if I dropped it down to right above the p-trap?

Don't do that.

I don't know if you can be certain that the smell is via that standpipe. You say that the smell is not correlated to your laundry use.

You could try pulling the washer drain hose, and putting a big rubber stopper in the standpipe between uses. See if the smell stops. If the smell continues to appear now and then, you would know that the smell is not from the standpipe.

https://hvchemical.com/rubber-stopper-size-chart/

Another thing that comes to mind is to figure out a dipstick that you could put down the hole. Normally, how much water is standing in the trap? When you get the smell, how much water is standing in the trap? This dipstick would need to be stiff enough to not follow around the U in the trap, but flexible enough to let you insert the dipstick.

 

[Lucas Keppers]

Don't do that.

I don't know if you can be certain that the smell is via that standpipe. You say that the smell is not correlated to your laundry use.

You could try pulling the washer drain hose, and putting a big rubber stopper in the standpipe between uses. See if the smell stops. If the smell continues to appear now and then, you would know that the smell is not from the standpipe.

https://hvchemical.com/rubber-stopper-size-chart/

Another thing that comes to mind is to figure out a dipstick that you could put down the hole. Normally, how much water is standing in the trap? When you get the smell, how much water is standing in the trap? This dipstick would need to be stiff enough to not follow around the U in the trap, but flexible enough to let you insert the dipstick.

So I do have a rubber insert caulked into the drain and have modified the hose for a tight fit. I still get the smell but it doesn't escape into the room as fast. I will get another piece to see if I can fully plug the drain. I really dont know what else it could be from, It's the only drain in that room and the smell is definitely emitting from that box. I have been underneath the house when it is happening and I dont smell it there. This house was flipped and all the sewer, water and electrical have been updated so there are no old sewer pipes visible to me. I will have to try the dipstick when it smells to see if there is water but there is some currently. Also it's about 5 foot of 2" pipe to the water in the trap.

 

[Lucas Keppers]

Don't do that.

I don't know if you can be certain that the smell is via that standpipe. You say that the smell is not correlated to your laundry use.

You could try pulling the washer drain hose, and putting a big rubber stopper in the standpipe between uses. See if the smell stops. If the smell continues to appear now and then, you would know that the smell is not from the standpipe.

https://hvchemical.com/rubber-stopper-size-chart/

Another thing that comes to mind is to figure out a dipstick that you could put down the hole. Normally, how much water is standing in the trap? When you get the smell, how much water is standing in the trap? This dipstick would need to be stiff enough to not follow around the U in the trap, but flexible enough to let you insert the dipstick.

Happened again about 11pm and there is water in the trap. I plugged it and less came out but as soon as I opened it there was no denying that the smell is coming from there. Took a picture and there are alot of suds in the water but the wife started the washer to try and get ride of the smell. Agian not sure if this is a back pressure issue and I need to add another vent out of the house to rectify this problem.

 

[Reach4]

If you are interested in measuring the pressure, I can tell you how. In fact, if you search this forum for open manometer, you can find such a description.

 

[Sam M]

I am not a pro by any means but is it possible you're getting some kind of back feed in the pipe? Since you mentioned it is a flip house with all redone plumbing, I would check that it is all connected properly and corners weren't cut.

 

[Lucas Keppers]

I am not a pro by any means but is it possible you're getting some kind of back feed in the pipe? Since you mentioned it is a flip house with all redone plumbing, I would check that it is all connected properly and corners weren't cut.

As far as the above ground goes, it's all connected properly besides the vent to the roof being undersized. Underground I would have to run a camera through it to double check. I have a good spot to run another 2" vent but it would come out of a vent for the attic. Dont want to punch another hole in my tin roof and this way it wouldn't build up in the attic either. I will try the manometer method first as they are only $35 on Amazon.

 

[Jeff H Young]

some how your trap isnt creating a trap seal. sealing around the drain hose dosent fix it

 

[Reach4]

As far as the above ground goes, it's all connected properly besides the vent to the roof being undersized. Underground I would have to run a camera through it to double check. I have a good spot to run another 2" vent but it would come out of a vent for the attic. Dont want to punch another hole in my tin roof and this way it wouldn't build up in the attic either. I will try the manometer method first as they are only $35 on Amazon.

My method costs only the price of a length of maybe 10 ft of clear plastic tubing. If you know somebody on an oxygen machine at home, they throw away 30 or 40 ft pieces monthly. I presume you have a clear drinking glass or glass jar.

An electronic manometer could be fun. But you will still need that 10 ft of tubing, unless that is included. The numbers are that the venting should keep pressure or vacuum to no more than 1 inch of water column, and that the trap should have a 2 inch or more seal. One inch of water is 0.249 kPa or 0.036 psi. Make sure that the scale is low enough on your electronic manometer to not be too big for such small pressures. Accuracy is normally specified as a percent of full scale, if there is a spec at all.

Be sure to blow out any water after passing the tube through the water seal in the trap and before hooking the tube to the manometer.

 

[Bannerman]

I have a good spot to run another 2" vent but it would come out of a vent for the attic.

If you are able to work in the attic, the additional vent pipe you install from the laundry area, will usually run horizontally (with a 1/4" per foot slope) to T into the existing 3" vent stack already protruding through the roof. This will then not require an additional roof penetration.