2 sinks meet hrztl @ dbl elbow, need one moved, which fitting is appropiate

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reevesk3

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Background….have a 2nd floor townhouse bathroom (shared stack) that I would like to move the drain to accommodate the new vanity. Currently, my drains meets with the neighbors drain horizontally at a double elbow which then travels horizontal again to the main stack as you can see from the pics. I would like to have the drain down that wall centered w my vanity. Do I just use a Tee and be done with it or ??…..also what’s pictured is a 3” copper drain and a 2” relief vent that ties into it.
thanks in advance
 

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wwhitney

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My initial thoughts:

- I'm surprised that adjoining townhomes could share DWV, not sure on the rules on that. If it is allowed, it may be that any new/replacement work in the common wall will have to be all in metal rather than plastic, something to check.

- I was going to say that a double elbow isn't to be used horizontally like that. Then I recalled that the IPC allows quarter bends to be used horizontally on fixture drains, like for a lav. But it won't be a fixture drain once they combine, so I'm still thinking the double elbow is not to be used like that. Bears checking, although likely moot as you'll likely have to remove it.

- If there's not a vent for the lav(s) upstream of that double elbow, then the vertical offset of the combined drain at the san-tee violates the trap weir rule. The top of of the side entry of the san-tee (the vent connection) has to be at a higher elevation than the bottom of your sink trap outlet.

So assuming that you can't/don't want to cause your neighbor to change anything, then I think you need to raise the san-tee at the stack to fix the trap weir rule violation. Then replace the double elbow with a combo, since you want to move your lav to the left.

If you could get your neighbor to install an AAV on their lav, and if you install an AAV on your lav, then you could omit raising the san-tee at the stack, although reliance on AAVs is a less robust solution.

And I'm assuming nothing is draining down the stack from above.

Cheers, Wayne
 

reevesk3

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i guess i should have given more background.....This townhome is in Mich and Im the owner. There are no rules other than code so i guess there is but Im allowed to replace anything however i can.....The plumbing work that you see is original from 1969 when the home was built. And yes this is the top of the stack. From whats pictured on up is all vent to the roof.....also, my neighbors are compliant to anything i suggest.....thx
 

wwhitney

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I should mention that one alternative to raising the san-tee or the AAVs is to cut in a revent between the old double elbow/new combo and the vertical offset. That would let you avoid dealing with the san-tee, although you'd still have to cut into the stack higher up for the revent.

Cheers, Wayne
 
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