Adding garage utility sink

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HudsonDIY

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Greetings all, I hope everyone is doing well.

I'm considering adding a utility sink in my garage. My wife is tired of me making a mess in her laundry sink. I'm sure some can relate.

What I'd like to do is tap into an existing waste pipe in the wall which handles a double vanity sink on the opposite side of the wall. The current set up is a pipe from each sink in a cross into a vent stack. Each sink has a p trap and AAV. My question is can I tap into one of the existing drain pipes to add the utility sink on the other side of the wall? I would use the exact set up with the p trap and AAV. I've attached a picture of one of the existing sink drains and a diagram of what I propose to do. Can I tap into the existing drain pipe or would I need to run a new pipe into the vent stack?

Thanks in advance for your replies,
 

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Reach4

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Are you saying the photo shows the sink that would share the drain with your new sink?

Is that shared drain pipe 1.5 or 2 inch?
 

HudsonDIY

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Reach,

There is one sink on either end of the horizontal cross in my terrible diagram, Sink 1 and Sink 2. Both sinks have the same set up with p-trap and AAV like in the photo, as would the new utility sink. They both run into the wall and then dump into a 2" pipe on either side of the vent stack. I need to add a third sink on the opposite side of the wall into this "somewhere". If I could tap into one of the horizontal 2" pipes with a Y that would be preferable to ripping into the wall more and adding another connection to the vent stack. I think that may be more than I want to get into.

Thanks,
 

Reach4

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The sink in your photo has an AAV, so it does not need an additional vent.

After thinking about this some more, it is possible that the vanity sink(s) provides the wet venting for the toilet. You would not be able to share the drain under IPC code in that case I think, despite it working fine in practice. I am not sure.

https://wabo.memberclicks.net/assets/pdfs/Plumbing_Venting_Brochure_2018.pdf Note in the wet-venting stuff, some applies only to bathroom group stuff.
 

HudsonDIY

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The toilet is across the room on the other side. Without ripping up the floor it's impossible to tell where it connects to the rest of the waste lines. There's also a shower on the same wall with a floor drain and a jacuzzi on the other end of the room which also goes into the floor. Since I don't see another vent stack going through the roof in that area and there is no obvious vent in the attic I'm guessing they connect to the same vent stack under the floor. I have a clear line of sight though garage access to the attic and that's the only stack I see.
 
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