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I have a new log house and the plumbers didn't want to put a hole in the roof, so they vented my drains with a stutgard(?) for air exchange and flow. Now there is a septic/mehane smell in our kitchen. I have not had any problems until now, just in the kitchen on 2nd floor. We have a septic tank and I am just puzzled.

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The German company ewo Stuttgart may be what you're talking about. A photo of the install would help a lot. It could be the wrong type of valve was fitted. – Bryce Dec 21 '13 at 7:04

A stutgard? I assume this is a brand of air admittance valve (AAV)? This is basically a one way air valve that allows air into the vent to break any siphon action on the trap seals, but supposedly prevents sewer gases from coming out of the vent into the house.

All the AAVs I've seen involve a lightly sprung wafer valve mechanism. They can sometimes become wedged slightly open due to debris or poor fit. Usually manually operating the wafer will free it so that it works normally again. You should be able to access the AAV itself, they are supposed to be installed in an accessible location for this reason. You may need to improvise a tool to manipulate the actual valve mechanism.

These devices have never struck me as completely gas tight when closed, it's not hard to imagine some small amount of gas could filter through enough that someone sensitive to such odors might detect it even when the AAV is operating normally. This last bit is strictly my opinion and disagreement from others is entirely possible.

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I have heard that if a drain is not properly vented that something like a toilet flush will suck the water out of the trap to find itself a way to vent. – Jack Nov 30 '13 at 2:12
What Jack says is quite true. I would hope new construction would not be so badly vented, but I suppose anything is possible. Some people would claim that the use of an AAV is not proper venting. They could have a point, it is not allowed under some codes. If it were not doing it's job, a toilet flush could suck out the trap seal. If the cause is a disrupted seal, the odor should be more evident at the sink drain. If out of the AAV, the odor should be more evident in its immediate vicinity. – bcworkz Nov 30 '13 at 21:22
I just reread your question, I was thinking one sink, one vent. There are no through the roof vents for ALL the plumbing in the house???!!!! Everything should be guaranteed for a year on new construction, and I hope this plumber has his insurance paid, there should be at least ONE vent that can be added. That may mean demo and repairs, but this outfit cant get off that easy. You may need to go down the pecking order though, GC first, then he gets to the plumber, and so on.... Do not leave this set!! This should not be your fix in a new home... – Jack Nov 30 '13 at 22:58
OMG! I was thinking the same thing, one AAV in the kitchen. If the entire house uses these things that is not good at all. They should only be used when a roof vent is physically impossible or at least extremely difficult, such as an island sink. Even then, foot vents could usually be constructed. Check what the local plumbing codes allow in this respect. This will tell you how much of a case you can build for installation of a proper venting system. Even if AAVs are allowed through out, the system is obviously not working. – bcworkz Dec 1 '13 at 19:30

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