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I am trying to tie in a new kitchen sink into an existing drain pipe currently servicing a bathroom on the other side of the wall. Here's the conceptual schematic of what I am trying to achieve: enter image description here

And here's what the situation looks like in reality: enter image description here

I am trying to figure out if I can avoid dismantling the existing T-Junction going into the bathroom and installing a new one for the kitchen in that 8" length of pipe, right above the existing junction.

Is this possible/good idea? For example, could I cut out most of that pipe and replace it with stuff like this?

https://www.homedepot.ca/en/home/p.1-12-in-abs-sanitary-tee-10bag-hub.1000109027.html

https://www.homedepot.ca/en/home/p.tubular-drain-connector-15125.1000120040.html

That no-hub coupling says that it works for 1-1/2" or 1-1/4" drain pipe. Does this mean that it can take the existing 1-1/4" drain pipe on one end, and the new 1-1/2" ABS pipe on the other?

It seems that I'd need to fit 2 no-hub couplings and one T-Junction in that 8" length of pipe. Is that likely to work, or is the length insufficient?

EDIT: How much pipe do I need to leave in order for a Fernco coupling to grab it reliably?

Any advice would be greatly appreciated.

  • It is understandable that you are focusing on fitting in the new entry point with the least disruption and trouble, but be sure you position the new entry point at the right height so that the drain from the planned new sink will be above it and so will drain into it. – Jim Stewart Feb 23 at 12:20
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From a code perspective it's hard to say because they vary quite a bit. For specific details about that you could always make an anonymous call to your local municipality. On to practical stuff, you can do what you have proposed. Pipe is measured by the inside diameterenter image description here That being said your pipe is inch and a half. For the rubber couplings, I always bring a piece of the pipe in with me and physically make sure that it fits. If you can get these Fernco couplings, they work wellenter image description here Always Clean, chamfer and deburr your pipe. If you find 8 inches is not enough space you could always cut further up and just pick up an ABS 45.

  • Looks like he has copper tubing used for the drains. Is copper tubing classified as to size and wall thickness the same way as the materials normally used for drains, i.e., cast iron, PVC, ABS ? – Jim Stewart Feb 22 at 11:53
  • When talking about sizes, the wall thickness is less important. What is important, depends on if it's piping or tubing. Pipe is ridgid tubing is flexible. So copper pipe is measured inside diameter and copper tubing is outside diameter. For example 5/8 tubing fits inside 1/2 " copper fittings. – Joe Fala Feb 22 at 12:14
  • I guess the short answer is yes. Lol – Joe Fala Feb 22 at 12:15
  • What is the history of use of copper piping for drains? This is a premium material and with sweated connections would presumably last a long time. (Of course, waste water could be acidic (vinegar is a standard household product) and would this mobilize lead from lead solder joints?) What about cost compared to standard materials? The only problem I can think of is corrosion from chemical reactivity with certain kinds of cleaning products. – Jim Stewart Feb 22 at 13:09
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    Copper drains aren't really a thing anymore due to the cost. It wasn't always in such high demand and was much cheaper then it is now and easier to work with then lead pipes. Household cleaning and vinegar don't have a constant presence long enough to effect the copper or the solder. Furnace and boiler condensate however, do. This came up in another post on here recently but I don't know how to link it in this comment. Condensate is about the same pH as vinegar and it will eat the pipes. But it takes a long time. Cleaning products are often followed by water and thus have a negligible effect. – Joe Fala Feb 22 at 13:38
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It looks like you have 1-1/2" DWV copper drain pipe. You could rip out all the accessible copper pipe and fittings and replace it with ABS, using two Fernco fittings for the transition, but I would stick with copper -or brass- for the additiional TEE (what you refer to as a T-junction) fitting for your new kitchen sink trap arm. But this is only possible if you have some vertical play or movement in the existing vent portion of the pipe, above the new tie-in. If you find there is no play and no way to lift the vent than you may need to resort to using one Fernco fitting located just above, and in addition to, the new TEE. There should be about a few inches of copper pipe left intact above the existing bathroom trap arm TEE fitting with which to sweat the new fitting on to. Then, sweat a few inches of copper pipe (a stub) above the new TEE so it just meets the bottom of the existing vent pipe. Slide the Fernco up the vent pipe all the way before sweating the stub on to the new TEE. Once it has cooled slide it back down to cover both halves of pipe. Tighten and test. Make sure to first measure the height allowance for the new sink trap arm so it will meet the location of the new TEE. Allow for some slope for the new 6" trap arm.

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