Sewer smells from washing machine drain line

Old 06-22-11, 12:47 PM
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Sewer smells from washing machine drain line

Hi All,
I am new to this forum and new to plumbing. We just bought a house that was built in 92. We live outside of the city and it turns out there are no plumbing inspections for homes built. So as it turns out most of our plumbing is likely not to code. The major concern was that all of our vents are vented to the attic. There are 2 3" pipes with studor vents on them and another 2" with a studor AAV (this is the one in the pic). Both plumbers and the inspector seemed to think that they were working just fine. However, my washing machine is giving off sewer smells. The area that the washing machine is, is very far away from the rest of the plumbing in the house and I think that the washing machine has its own vent and is not tied into anything else.

Anyway, as you can see in the diagram (blue) the vent is on the wrong side of the p-trap. We have thought about coming up on the sewer side of the p-trap and then coming over and tying into the vent (Red), however there is little space due to conduit networking throughout. We should be able to make it fit if this is the route we want to take, but still deciding (hopefully you guys can help). The other idea that we had was to just install an AAV on the sewer side of the p-trap (green) and cut off the vent that goes into the attic. If we go this route, how high doe the p-trap need to be? Manufactures say a minimum of 4" above p-trap, but then I also see that they like them 18" above the drain?

Do you guys have any input on this? I know, I know, that we need to get those vents to the outside, but that is going to take some time and money, and are looking for a fix that will suffice for now.

Thanks for your help

Old 06-22-11, 01:18 PM
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Is there any other plumbing draing into these pipes?

If its just the washer there, and nothing else drains into the lines in the drawing, then the studor vent is correct if it is the green square you have.

In all reality that pipe that goes to the attic should be where the studor vent is. Thats if there are no other fixtures draining into it.

Note: The studor vents should be above the flood plane of the fixture.

That red line would be correct also, but it should tie in above the washer. ( Above the flood plane of the fixture. )

Possibly leave the studor vent. ( green square ) and cap that line that goes up in the attic. The water may be pulling out of the trap because of that vent. What I mean is that vent makes it easier to pull the water out of the trap then to have the sutdor vent open. I hope you understand what I am saying.

Mike NJ

Last edited by lawrosa; 06-22-11 at 02:27 PM.
Old 06-25-11, 12:44 PM
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Your drawing depicts what is refered to as a running trap. Not common in my part of the country. I can see how on a washing machine drain with a quarter inch per foot fall that it could easily be siphoned as the last slug of water passes through it. This would explain why you are getting sewer gas back into the home. If this were my home I would remove the running trap, and cut the original stand pipe below the floor and cap it off. I would then install a sanitary tee on the existing vent line at an elevation just high enough for a new P-Trap to be installed as close to the floor as possible. I am not a fan of air admittance valves (they are not allowed by code in a lot of places) If it were possible to extend the vent through the roof, all the better.

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