Sewer smell from overflows when using sinks

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Marc1984

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We have a fairly new house that we bought in november 2017. We had heavy rain 2 weeks ago and since then, we have noticed unpleasant smells in multiple sinks when running water. It seems like it is coming out of the overflows of sinks. We can also get the smell from the bathroom sink when draining a full bath.

I suspect the vent system to be the issue but there are no gurgling noises coming for any toilet or sink. It is as if when running water, some sewer gas was able to make it's way in the overflow of the sink for the duration of the use. Could that be due to a high pressure in the vent stack? If so, could it be from the council drain pipe pressure?
 
I forgot to mention that it is :
- not the water smelling like sewers. I have run the water in plastic containers without getting the smell
- not the smell of residues in the P-Trap. I have run baking soda and vinegard in all sinks and checked for hairs.
 
Hi TomFOhio,
Yes I'm sure it is not from my hot water. I have run hot water in a jar already without any smell and it doesn't smell when we run a bath or use the shower. The smell really only comes from the sinks (3 of them located on 3 different levels of the house) when in use.

I am a bit lost as to what it could be...
 
Good.. That rules out the anode rod on your water heater. If these are lavatories try cleaning out the overflows on the
sinks. Maybe run a wire in them. Clean the sink and with the cleaner in it fill it up to the overflow and see if it goes down.
Sometimes that can cause smell at a sink.
 
Thanks for the pointers. I have put baking soda and vinegar in all P-traps and overflows and have let all lavatories fill up until they reached the overflow. They all empty really well and did not seem to be clogged up.

Any ideas on what could be off with the vent system? I experienced it again last night when we emptied the bath and we got a really strong sewer smell coming out of the bathroom sink overflow. There's no problem draining so the vent can't be completely obstructed. It is as if the water running down the pipes was forcing some sewer gas up. That seems to me possible only if there is :
1- not enough of fresh air supply from the vent stack or
2- an over pressure in the vent system.

Does that make any sense to you? Where should I start looking since this as not always been there since moving in the house...
 
Thanks for the pointers. I have put baking soda and vinegar in all P-traps and overflows and have let all lavatories fill up until they reached the overflow. They all empty really well and did not seem to be clogged up.

Any ideas on what could be off with the vent system? I experienced it again last night when we emptied the bath and we got a really strong sewer smell coming out of the bathroom sink overflow. There's no problem draining so the vent can't be completely obstructed. It is as if the water running down the pipes was forcing some sewer gas up. That seems to me possible only if there is :
1- not enough of fresh air supply from the vent stack or
2- an over pressure in the vent system.

Does that make any sense to you? Where should I start looking since this as not always been there since moving in the house...
Sounds to me like the trap is being siphoned out allowing sewer gas smells. This of course would mean venting problems if traps are being siphoned out.
To try to confirm this, I would I select an offending sink that is equipped with a trap plug. Let water flow slowly for a minute to insure trap is full of water. Remove trap plug and observe how water is in a full trap. Now when you duplicate the smell problem, by whatever means, open the trap plug and check if had enough water to seal the sewer gases from entering the sink/room.
Before and After.jpg
 
Thanks DieHard. Sounds like a sound way of troubleshooting it. Will give it a go tonight.
 
I have noticed that our sink overflows can smell really bad. Like sewage. When it's really bad I can just put my nose near one of the Overflow holes and give it a whiff to notice the smell is pretty strong. In my case it seems to be due to gunk and funk growing inside the Overflow exacerbated by warm weather. I have several things that I do to kill off the offensive smell. It doesn't go away without a fight! It affects both sinks on two floors around the same time of the year.
 
I have made the test last night and I got the same amount of water out both times. Also, I realized that if the P-Trap was syphoned out, it would stink all the time until it is replenished with water, which is not the case.

What puzzles me even more now is that I could not get the sewer smell while I had the P-Trap dismounted...note that I drained the bath to try to recreate the smell (see below new theory).

What if the vent stack was too far from the sinks and did not have an independent vent reaching to the main one? With enough water being flushed in the system, it would eventually suck out the sewer gases from the individual branches but it would eventually fill back up. I noticed yesterday ,as I was running the tap, that I could feel bubbles in the P-Trap from the water turbulence of the water running. Could this create a passage for the gases to slowly come back up? It would stink when not used for a while and with enough water passing through it would create a negative pressure that would "activate" the main vent.

If this is the case, an air admission valve added to each sink would probably prevent the smell.

This is starting to be far fetched but still keen to have your opinion on it.
 
I have noticed that our sink overflows can smell really bad. Like sewage. When it's really bad I can just put my nose near one of the Overflow holes and give it a whiff to notice the smell is pretty strong. In my case it seems to be due to gunk and funk growing inside the Overflow exacerbated by warm weather. I have several things that I do to kill off the offensive smell. It doesn't go away without a fight! It affects both sinks on two floors around the same time of the year.
That's interesting. I have used baking soda and vinegar in all sinks AND overflows and it seems to have got rid of the smell for 1 day...it was back after. In my case, we have been in the house for less than 1 year and I have checked P-Traps for gunk and they were really clean. Still interested in knowing what you do to clean them?
 
I have made the test last night and I got the same amount of water out both times. Also, I realized that if the P-Trap was syphoned out, it would stink all the time until it is replenished with water, which is not the case.

What puzzles me even more now is that I could not get the sewer smell while I had the P-Trap dismounted...note that I drained the bath to try to recreate the smell (see below new theory).

What if the vent stack was too far from the sinks and did not have an independent vent reaching to the main one? With enough water being flushed in the system, it would eventually suck out the sewer gases from the individual branches but it would eventually fill back up. I noticed yesterday ,as I was running the tap, that I could feel bubbles in the P-Trap from the water turbulence of the water running. Could this create a passage for the gases to slowly come back up? It would stink when not used for a while and with enough water passing through it would create a negative pressure that would "activate" the main vent.

If this is the case, an air admission valve added to each sink would probably prevent the smell.

This is starting to be far fetched but still keen to have your opinion on it.
Well at least we eliminated one possibility.:)
To the best of my limited experience on these matters I could only guess that in order to get bubbling back up from the sink drain line would possibly be due to the lack of air to allow it to flow properly. But draining your tub shouldn't cause any reaction in the sink drain unless the sink is being used at the same time.
 
I have used foaming (scrubbing bubbles) products before. Its easy to spray it into the overflow and it expands everywhere. Do it before bed for a few days and rinse it well each morning. I have also used spray tub and tile / soap scum products in the same way. I spray quite a lot so it's well saturated. It's a good idea to plug the hole after spraying so the product doesn't evaporate. I use a blob of wet toilet paper which conforms to the hole. Btw, have you tried vigorously plunging the sink while plugging the overflow?
 
Try getting on the roof and looking down the vents with a flashlight. Something may have built a nest in your vent. That is another avenue you can explore.
 
Or that heavy rain filled a belly in a horizontal vent line blocking the air flow? Best easy test I have found is weird but effective. Someone on roof hovering over vent stack. Take the trap off that sink. If you 2 can communicate thru that pipe in wall then your vent is open. If it’s full of water. The water blocks vibration and no noise gets thru. Check each sink affected then go into attic and see. You will see a belly that big. For some reason the old plumbers in my town strapped vents 1/2 as much as they should because “it never carries water”. As it was raining he said that. I try to control my body language but my eyes were screaming “dummy”. But more vulgar. Lol
 

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