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 Sewer smell when washer runs after sitting
Author: robhandyman (MA)

I relocated my washer and hooked the drain line to an existing line that comes from a sink. I put separate ptraps on the sink and on the washer. However, when the washer has not been used for some time (a day or two) I get this strong sewer smell the first time it discharges. After that initial discharge the smell goes away. The washer is on the other side of the wall and I made sure it had proper slope on the line. I'm thinking I should have only used one ptrap vs two. Any insight would be appreciated.

Thanks.







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 Re: Sewer smell when washer runs after sitting
Author: North Carolina Plumber (NC)

Both traps need a vent, a sink is not suppose to share a drain with a washing machine, the washing machine drain needs to be 3" as soon as it turns horizontal ( some areas can still use 2" ). I don't see a good way of fixing what you have there. Can you access the horizontal drain on the other side of the wall ? If you could get a trap and vent downstream of that wye and cleanout you could probably make it work, but it wouldn't be code compliant.

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 Re: Sewer smell when washer runs after sitting
Author: robhandyman (MA)

The horizontal drain goes across directly to the vent stack (with no access). The sink was there when I moved in years ago and never had any kind of an odor issue. I'm still confused why I'm getting the odor however. The code you mentioned is interesting to me since you can empty a washer into a sink. Is there a particular reason for it?

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 Re: Sewer smell when washer runs after sitting
Author: pbw (OH)

with the large discharge of the washer you may be pulling all the water from one trap, thus the sewer order.
as the north Carolina plumber said, a minimum of a 2" drain with a vent, a three inch drain would be better.

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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

people on this board should be careful when stating what a code does and doesn't say.
MA code allows 1 1/2 inch for a washing machine drain.... other juristricions do not.
anyway, you said the kitchen drain ties into a vent stack. what size is that stack and can you get access to it?
can you get us a picture of it?

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 Re: Sewer smell when washer runs after sitting
Author: steve (CA)

You also can't use a sanitary tee in that position.

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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

this is MA... any plumbing he does is illegal..

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 Re: Sewer smell when washer runs after sitting
Author: robhandyman (MA)

Everything in the house is pretty well
closed up. I'll check in the attic to see if I can measure it. The sink is a utility sink in the garage. Can anyone explain why this is happening and if using a single ptrap would address this issue? The alternative is having to open up walls and ceilings to do additional plumbing.

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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

none of this is legal... but.. if that sanitary tee looked straight up, had a short nipple in it, had another san tee on top with the side facing the back wall. ontop of that san tee put an AAV

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 Re: Sewer smell when washer runs after sitting
Author: North Carolina Plumber (NC)

If you can cut that wye and cleanout off, turn a 90 vertical in it's place, stack a pair of tee's to catch the washer drain first, then the sink drain, then an AAV atop the tees. The washer trap is running,meaning horizontal in and horizontal out. The inlet needs to be vertical and it needs to be directly under the standpipe, or at least needs a pair of 45's on the vertical to get up to at least 36" from the floor.
When you're flushing water down the stack it's creating both positive and negative pressures inside the piping. With that running trap it's much easier for the water seal to be lost and that's why you're getting an odor. An AAV will prevent any negative pressure, or vacuum from pulling the water from the trap.

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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

remember we are not allowed to use a trap adapter on the outlet side of the trap. so we must by MA code either install a cleanout under the sink or have a glued on trap with a union swivel in it so the bottom of the trap can be removed for snaking.
in any case, you are correct that either a vent thru the roof or an AAV must be incorporated in that mix of piping to eliminate syphoning.

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 Re: Sewer smell when washer runs after sitting
Author: North Carolina Plumber (NC)

Oh yeah, that's right. You don't use "toy" traps there . :) Leave the wye and cleanout, cut the 90 from the wye, put a tee in it's place, with the branch turned horizontal for the washer trap, then a st.45 in the top of the tee to get the piping vertical, tee for the sink trap then an AAV.



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 Re: Sewer smell when washer runs after sitting
Author: robhandyman (MA)

Ok. If I understand what you are recommending correctly, it would look like this sketch, correct? Are there any special requirements on the tees to make these connections? And thank you.

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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

close...
the lower drawing is almost correct.
face the lower san tee towards the washer and run the pipe thru the wall. put the washer trap on the other side of the wall with a standpipe.

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 Re: Sewer smell when washer runs after sitting
Author: North Carolina Plumber (NC)

Top picture is correct, you still have a running trap in the lower picture. You need to drop down vertically into the trap with your washing machine standpipe.

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 Re: Sewer smell when washer runs after sitting
Author: robhandyman (MA)

So then this would be OK?





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 Re: Sewer smell when washer runs after sitting
Author: exapprentice30 (MA)

Replace the 90 with a sanitary tee and and a piece of pipe in the top for your vent. If you have room you can make it longer than your standpipe. you can use a sanitary tee on its back horizontally looking up for the vent too.



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 Re: Sewer smell when washer runs after sitting
Author: exapprentice30 (MA)

[www.youtube.com] You can see a non vented vs a vented trap.



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 Re: Sewer smell when washer runs after sitting
Author: robhandyman (MA)

I guess I need to bring the line back outside the wall, but if that's needed then so be it. There's just no room in the wall to put the ptrap and venting. Most will be hidden by the washer so it's not too bad.





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 Re: Sewer smell when washer runs after sitting
Author: packy (MA)

now you have the concept.. i would try to get the AAV higher if possible and hide it behind an access panel.

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 Re: Sewer smell when washer runs after sitting
Author: sum (FL)

your washing machine drain is "draining" uphill up that horizontal pipe where the cleanout is, then when the washer is emptying the positive pressure of the pipe is pushing that water up, then splitting the flow into the top and branch of the sanitary tee, your sink is draining into a sanitary tee on it's back with a branch in the reverse direction and probably your sink is also dumping into your washer horizontal line if it's not full of water. When the washer pump works it probably blows whatever air pocket there is in that line up your sink and pushed that sewer gas into your living space. Once the water starts running that entire contraption is flooded so no more sewer gas until things settle.

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