Greater time between flushes makes stronger gas smell

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J Blow

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We have what's basically a single level tiny house with a a private well and septic system - one bathroom. After sitting for a while (a day or so), a sewer/gas smell is present after flushing the toilet. The smell isn't present until you flush and a second and third flush produce a bit of a smell but definitely decreased. I don't really notice it after that but it could be for many reasons. We have a single vent but do have an RV dump up the line that I leave uncapped as it seemed like calling it created a smell, too. I ran a snake down the vent and believe that's clear but stumped on what the problem could be. I don't think it's anything like a cracked bowl or loose pipes as there's no smell until a flush

Ideas? Thanks.
 

J Blow

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We have what's basically a single level tiny house with a a private well and septic system - one bathroom. After sitting for a while (a day or so), a sewer/gas smell is present after flushing the toilet. The smell isn't present until you flush and a second and third flush produce a bit of a smell but definitely decreased. I don't really notice it after that but it could be for many reasons. We have a single vent but do have an RV dump up the line that I leave uncapped as it seemed like calling it created a smell, too. I ran a snake down the vent and believe that's clear but stumped on what the problem could be. I don't think it's anything like a cracked bowl or loose pipes as there's no smell until a flush

Ideas? Thanks.
I probably should have added that I have had a problem with the trap freezing under the tub but nothing pouring a little antifreeze down or hasn't immediately resolved.

Also, and maybe this was bad, but I ran a water down the vent stack for quite a while just to be sure nothing was plugged and kicked back at me. Seemed to be no issue with blockage.
 

Reach4

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Also, and maybe this was bad, but I ran a water down the vent stack for quite a while just to be sure nothing was plugged and kicked back at me. Seemed to be no issue with blockage.
Bad. But good that your test is telling you something.

Even if we imagine that the septic was full, the symptom should have been water coming out of your lowest drain -- maybe the shower or RV dump.
 

J Blow

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I think I would check the seal on the wax ring.


The question I have on this is why the smell only occurs after sitting a while and doesn't create an issue with flushes closer together.

Also, would a leaking wax ring do this ONLY during the flush or would a gas smell be present all the time?
 

Tuttles Revenge

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Pressure. You may have a slight clog in the line or in the system somewhere and as you add waste/water into the system the air has to eventually go somewhere, which should normally be your vent.. but if you have a gap in your wax seal, some will come out there.
 

J Blow

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Pressure. You may have a slight clog in the line or in the system somewhere and as you add waste/water into the system the air has to eventually go somewhere, which should normally be your vent.. but if you have a gap in your wax seal, some will come out there.

This makes sense to me but why would sitting for several hours be the cause for the gas smell versus every flush close together? Seems like it would be opposite - a slight clog will allow it to leak down slowly and dissipate the gas....or is that now how it works? I know why trap drying up creates the smell but this doesn't seem to be that.

If the wax ring was bad would that be an every flush thing or why just after sitting, too?
 

J Blow

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I'm going to try the peppermint test but I think I'll probably just replace the wax ring. Guess I'll probably run a snake down the toilet drain first. Seems like a good place to start.
 

WorthFlorida

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This makes sense to me but why would sitting for several hours be the cause for the gas smell versus every flush close together? Seems like it would be opposite - a slight clog will allow it to leak down slowly and dissipate the gas....or is that now how it works? I know why trap drying up creates the smell but this doesn't seem to be that.

If the wax ring was bad would that be an every flush thing or why just after sitting, too?
It would take a lot of gas to seep into the bathroom from under the toilet. Usually the toilet is caulked or grouted to the floor, therefore, I doubt it is a bad wax seal. The fix could be the vent in the house is blocked so gas from the septic tank cannot escape, (it's what Tuttles Revenge suggest), the septic tank needs to be pumped out and/or vent the septic tank.

Is this a new problem or always had the issue? Is the septic tank vented? Most are not and over time the gas builds up to a point it has no where to go, when you flush, at the end of the flush the siphon breaks and it's when to hear that gurgle noise. With gas pressure behind the flushed water, it's pushing against it and the gas will backup into the bathroom when the siphon breaks. It's why the odor is less with each flush.


A google search on "are septic tanks vented"
A Septic Tank's Vent
The tank and its plumbing system are sealed, which means the air inside is trapped. However, as the tank fills with waste and water run-off, the air needs somewhere to go – otherwise, the pressure it creates will halt the flow of waste and back up the toilets, etc.

1650314311419.png
 

Reach4

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I would be thinking of a camera looking for a belly, rather than the peppermint test.

Also, if the symptom does not occur when the outside cleanout is open, if you have one, that would be informative. I think most people don't have one on the way to the septic.
 

John Gayewski

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It would take a lot of gas to seep into the bathroom from under the toilet. Usually the toilet is caulked or grouted to the floor, therefore, I doubt it is a bad wax seal. The fix could be the vent in the house is blocked so gas from the septic tank cannot escape, (it's what Tuttles Revenge suggest), the septic tank needs to be pumped out and/or vent the septic tank.

Is this a new problem or always had the issue? Is the septic tank vented? Most are not and over time the gas builds up to a point it has no where to go, when you flush, at the end of the flush the siphon breaks and it's when to hear that gurgle noise. With gas pressure behind the flushed water, it's pushing against it and the gas will backup into the bathroom when the siphon breaks. It's why the odor is less with each flush.


A google search on "are septic tanks vented"
A Septic Tank's Vent
The tank and its plumbing system are sealed, which means the air inside is trapped. However, as the tank fills with waste and water run-off, the air needs somewhere to go – otherwise, the pressure it creates will halt the flow of waste and back up the toilets, etc.

View attachment 82802
You'd have to be pretty determined to caulk a toilet all the way around. Most people do not fully caulk a toilet for this reason. If your wax seal is broken you'd like to know. One way to know could be water showing up upon flushing, another could be sewer gas escape. You don't want the toilet itself to be a secondary seal.
 

WorthFlorida

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During the second or two of the gurgle when the siphon breaks is when gas can backup into the bathroom. From the picture above the gas or air should be going up out the the roof vent.
 

WorthFlorida

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You'd have to be pretty determined to caulk a toilet all the way around. Most people do not fully caulk a toilet for this reason. If your wax seal is broken you'd like to know. One way to know could be water showing up upon flushing, another could be sewer gas escape. You don't want the toilet itself to be a secondary seal.
Plumbers here in Florida seal the entire toilet and they seem to prefer to sit the toilet on a little grout. I've removed all three toilets in my current home, built 2007, either because of a remodel or redoing the floor. Each had grout. On a major remodel of two bathrooms, two different plumbers ask for grout to set the bowl. One was on the first floor slab and the other the second floor. I'm not saying it's better or a gap should be left, it's just the way it is done.
 
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