sewer gas smell in old house

Daughter bought a older home that had the kitchen remodeled. The kitchen sink does not have a direct vent to the roof but uses one of the pressure valves type devices. The device is under the kitchen sink in a corner of the cabinet against the very back wall. Now here's the strange part. There is what appears to be a yellow plastic sticking out of the pipe.
It's like they put a plastic bag over the pipe and then shoved the vent device over the plastic.
Unfortunately there is no way to run a real pipe vent up through the walls and out the roof. I could drill a hole through the 12" brick wall to the outside but that's a street/sidewalk side wall and would look terrible.
So before I take this apart...anybody have an idea what the problem is. (I do understand the principal of venting and the vacuum created by water running down the drain)
Also, a possible contributing factor. The sink drain has the LONGEST tail piece I've ever seen. It makes the P trap assembly extremely deep reaching almost to the bottom of the sink cabinet before it goes back up and then horizontal into the drain. It's got to hold more water than any P trap I've seen in a residential installation.
Please help, the smell is bad and you waste a lot of water running in the sink to remove the smell. Although the smell could be coming from the laundry sinks in the basement directly below.
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FireBrick wrote:

They may have made the trap deep in order to try and solve the problem of self-siphoning (guess).
I'm guessing the pipe where the vent device is connected is iron. Re-do the connection to the device using a No-Hub (Fernco) coupling to avoid whatever the yellow thing is and prevent leaks there.
When the sink drains a large volume, you should be able to hear the vent device suck in air and/or chatter.
Shine a bright light down the sink drain and see if there is water in the trap. If there *is*, then the trap is not allowing sewer gas up.
It *could* be that the long tailpiece is full of gunk (tech term) which is moldy and emitting the odor. Could try bleach to kill it but probably have to take tailpiece out.
Jim
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Thanks Jim...I'll check that tailpiece and P trap. But the drain is 2" PVC which goes down and obviously connects to some iron somewhere inside the finished ceiling....
While we can't find any evidence of water leakage...wonder if the transition from PVC to Cast seal is good...
Oh and BTW: Here in Chicagoland the tech term for that stuff that builds up inside drains is 'smegula'. <wink>
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Don Young
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