Sewer smell from 3 bathroom sinks

[Mred.Mcgee]

What am I missing ? I have a lot of time in on this one, and I need some help. I am having a problem with Sewage odor (sulfur) coming from 3 bathroom sinks in my new home. Only 3 of 7 bath sinks in the house with the smell issue. The problem only occurs when you run the water. The traps is not/ does not empty. This is a new home with a septic (gravity 2 chamber with infiltrator drain field, sandy soil, no drainage issues). I didn’t have the problem until about 6-7 months after I’ve lived in the home. I am guessing once we started to accumulate more solids/ gases in the tank, the smells began. When the running water stops the smell stops. I’m sure its coming from the sink drain, I have a good nose. The traps are not dry, and they are not getting siphoned. I am guessing maybe there is back pressure of sewer gas making it thru up thru the trap, and not exiting thru the vent properly? The bathroom sinks with the smell are on the back left side of the home, on the same side as the septic exit (1st and second floor). The first floor bath sink with the smell issue does not have a stack vent since it was not possible (it was difficult for the vent routing upward because of 2 story block construction). Same with the kitchen sink, but no issues on that one. Contractor doing rough told me to install an AAV. The AAV is 4 inches above the drain. I did the finish plumbing, Licensed plumber did all the rough. There are no backups, no toilet gurgling, everything drains very well. I was my own GC during construction and hired out the trades for a lot of the work, so I am intimately familiar with the construction, and I have tons of pics, and I was there every step of the way.

I am looking for suggestions, and any good ideas on what to check/ troubleshoot next.

I have attached some diagrams / pics. Thanks Ed

I have tried the following:

-Ran Baking soda/ vinegar thru the drains.
-Cleaned the drains / traps with bleach
-Ran Liquid Plumber thru the drains.
-Cleaned the sink overflows/ bleach
-Inspected above and below roof vent with pics. Drone & Small Inspection camera. (See pics).
-Took the traps and under plumbing drains apart and cleaned, brushed. No leaks.
-Examined traps with flashlight behind trap to see water level, while other water running in showers and multiple toilet flushes. Little to no water movement in trap.
- Examined the trap while water running in sink, looks normal.
-Put a 5 ft riser on my cleanout to make it a temporary vent.
-Increased the size of trap seal from ~2" to 4”. I thought I had it licked on this one ! no luck :-(
-Under sink plumbing is not greater than 24”
-Tested the AAV, replaced.

 

[Reach4]

Looking at M BA, I expect that the venting for the two lavatories is a little different than your sketches.

With a through-the-roof vent on that bathroom it is hard to see how pressure could be enough to break the trap seal.

There is a way to check the pressure in your drain pipes if you are up to it. https://terrylove.com/forums/index.php?threads/steps-for-diagnosing-sewage-smell.59599/ #4 and https://terrylove.com/forums/index.php?threads/sewer-gas-coming-up-through-toilet-bowl-itself.94812/ #5 get into it.

 

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[Jeff H Young]

tough one If I could see how it was plumbed I might help but these drawings are a bit hard to interpret

 

[Reach4]

If it were not for that TTR (thru the roof) vent I would suspect a drain line with a belly in it. But that TTR vent should work around that for the master bath, I would have thought.

The way to find a pipe belly is with a camera. Drain lines should not have much standing water, except in a trap.

 

[Jeff H Young]

Somethings wrong maybe you just got a stink from the overflow of the sink they sometimes trap water and get nasty, its fresh in my mind because another guy was having problem with his sink giving off stink.
If nothing is backing up and its vented properly shouldn't have smell

 

[Mred.Mcgee]

So I am still at it. I haven't scoped anything yet. Im trying to research that-- Maybe an inexpensive amazon camera attached to a drain auger is what I read that alot of DIY's do. I hope I don't have a belly under the slab. But I agree on the master bath sinks with the TTR Thru the Roof Vent as to why I am getting sewer smell. I have another thread going on regarding my overflow port on my drain being high and holding back water behind it to sit and ferment. I notched it so that any water that gets behind the port drains properly. Water gets behind the port even when regular draining/ not overflow. I also cleaned the overflow again, I have a small scope and didn't see any abnormality inside the sink overflow. See pics where I notched the sink drain overflow port.

I also took the trap and trap arm off. I felt a breeze (No smell), coming in. the TTR is directly above the sink ~ 10 Ft on roof, and I guess the outside wind was blowing down the vent. I re assembled the under sink plumbing and connected it back up. I didn't fill the trap and just observed for awhile. Slight breeze coming up and down the drain. Enough to flutter a strip of a tissue. (No foul smells) ( I know ingenuity at its best). I even flushed the toilet a couple times and I could hear the flushed water draining through the dry sink trap. It sounded normal. Filled the trap, and no smell, but Ill give it 24 hours to see if it returns.

 

[James Henry]

You make it sound like its the water that smells. If you do determine it's the water then just replace the aerator's on those faucets.
put the stopper in the sink and run the water, if it still smells then its your water.
On the other hand I have experienced strong back pressures on drains before so it's quite possible.

 

[Mred.Mcgee]

You make it sound like its the water that smells. If you do determine it's the water then just replace the aerator's on those faucets.
put the stopper in the sink and run the water, if it still smells then its your water.
On the other hand I have experienced strong back pressures on drains before so it's quite possible.

Thanks James. I'm almost positive it's coming from the drain area. I'll take a look at the aerators. Any idea what causes the strong back pressure on drains? This is a septic.