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Doing a kitchen remodel and I tore out the sink, the sink cabinet and the sheetrock behind the sink and this is what I'm seeing:

enter image description here

It was a double sink (two sinks side-by-side, with two drains but with both sharing the same faucet). I'm replacing it with a new sink that will only have one (1) drain.

As you can see in the picture, there's something interesting going on here with the existing drain system:

  • both drains wye together; this makes sense to me
  • what in the name of all that is holy is going on with that big copper loop that is connecting both the drains from above?!? Is it for drainage/air flow? How does it work?!

The main question here is: what do I need to do so that my new sink is only using the left drain (the one with the metal/brass p-trap) and so that the right drain is completely capped off? Can I just make a cut on the right branch coming out of the wye and then another cut right above the left p-trap, and cap them at both places? Will this cause issues with airflow that the big copper loop was trying to prevent?

In other words, my plan (unless someone here tells me I'm misunderstanding) is to do this:

enter image description here

  • Anything that is red will be removed (I will install a cap right above the right branch of the wye that is coming out of the floor)
  • The purple blob represents an AAV I will install about a foot above the left drain, which I intend to keep for the new sink
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  • 3
    newer seen copper pipe used as drain (what a waste of money
    – Traveler
    Apr 13, 2023 at 1:05
  • Whiskey. Tango. Foxtrot.
    – Huesmann
    Apr 13, 2023 at 14:51

3 Answers 3

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Cut out both tees and everything above them. Replace the left tee with an elbow, coming out into the cabinet and put an AAV and trap adapter there, inside the cabinet not inside the wall.

Replace the right tee with an elbow and a cleanout accessible from the cabinet.

Alternately if you can replace it all with a new 2" PVC from the basement coming up in the right place, do that, still with the AAV in the cabinet not the wall.

Finally is there a vent stack anywhere accessible from the basement? You could use Island venting instead of mechanical.

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  • Thanks @jay613 (+1) everything you say makes sense. Just two rookie questions though, if thats OK: (1) none of the other sinks in my house have an AAV underneath them (inside the vanity cabinets). Are these being vented by some other system? I'm guessing they're all connected to this vent stack that you mentioned? Some type of central vent pipe that exits the house? Apr 13, 2023 at 10:57
  • And (2) I found this article on Island venting vs AAVs. I'm guessing that Option 1 in that article (Island venting) would be possible if I could find that vent stack and tie into it? Thanks again for all the help here! Apr 13, 2023 at 10:57
  • Not necessarily one central vent. There's a pipe that rises from the drain and goes up through the roof where it's open. Each room can have its own or more than one but usually the bathrooms and kitchens are arranged so they can share a vent pipe. In a small house there might be only one EG the bathroom above the kitchen share one vent.
    – jay613
    Apr 13, 2023 at 13:06
  • If you can find a vent stack hopefully you can use it. It's simple in concept but the details are not simple, so consult a plumber if you're going to try that. Water that gets into the vent has to drain into the drain, and doing that with a pair of pipes running horizontal under the floor requires some planning.
    – jay613
    Apr 13, 2023 at 13:10
  • diy.stackexchange.com/a/151962/65210 Interesting reading on just one little detail of the island arrangement ... what bits to use for the top bend.
    – jay613
    Apr 13, 2023 at 14:46
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This was before they invented the drain vent or the plumber was a artist. LOL

The u-shaped was acting as vent, where one sink was vented by the other sink. Since you are planing to use only one sink you will have to modernize and install a vent pipe or use AAV.

Using copper pipes as drain in new to me, and I thought I have seen it all. Today people use aluminum wiring just because the copper is to expensive.

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  • Thanks @Ruskes (+1), so to confirm: (i) I can make a cut on the right branch leading up out of the wye (the branch leading to the right drain) and cap it, (ii) then about a foot above the left drain (the one I want to keep) I can make another cut, which will remove the entire U-shaped/loop vent. Then (iii) I can instal an AAV on top of that 2nd cut (about a foot above the left drain which again I am keeping). This will work OK for me? Thanks again! Apr 13, 2023 at 1:50
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    @hotmeatballsoup Attention soldering copper with torch so close to wood will be a fire problem. Since the right branch is no longer used and not in your way just leave it alone. Your cut is just above the AAV where you can also cap of. The second cap is on the protruding pipe on the right, far away from the wood.
    – Traveler
    Apr 13, 2023 at 2:59
  • I don't quite get " one sink venting the other sink ". Was this an actual concept at some point? If the flow of water is not to empty either trap then what, are we hoping the large cushion of air in the high loop will decompress to absorb the negative pressure? Was there any theory behind this? I've never seen this before, it looks almost like someone saw an island vent and tried to replicate it from memory.
    – jay613
    Apr 13, 2023 at 13:03
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What you originally planned will work, however remember that the AAV should be accessible as it can require maintenance.

Do air admittance valves need maintenance? There is no one definitive answer to this question as it depends on the specific valve, the type of air admittance system it is, and how often it is used. However, generally speaking, air admittance valves will need to be cleaned and inspected periodically in order to ensure that they are functioning properly.

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