New undermount sink depth & how to tie into cast drain.

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  #1  
Old 12-23-20, 04:11 PM
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New undermount sink depth & how to tie into cast drain.

Getting new counter tops and want to get under mount sink.
The problem is the old sink has 7 & 3/4in from the lip to the bottom of the sink. 9 & 3/4 from the lip to where the threaded part for attaching the P trap.
When putting in under mount sink this will lower the drain etc.
Where the P trap etc. ties into the wall is old cast pipe that runs inside the wall a bit till it reaches the stack. To change the cast pipe in the wall would involve a lot of demo and effort.
I had a thought when writing this about capping off cast drain and run a new PVC drain inside the cabinet to the stack and then tie in the new drain. It doable as the cupboard beside the sink cupboard is a corner cupboard and open.
If this is acceptable then that leaves how to tie in the new pipe into the old cast stack?
 
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Old 12-23-20, 05:57 PM
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Can you post a picture of the area showing the drain pipe.
 
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Old 12-23-20, 06:35 PM
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You can run through the cabinets, but I would suggest that you use 2" pipe, sloped at 1/4" per foot. This will ensure that your trap arm remains vented as long as it is no more than 8 feet from the sink trap to the cast iron stack.

As for tying into the stack, you will need to cut out about 16" of the stack... you will need to support the cast with several straps above and below the cut so that it doesn't slip down when you cut it. If you can snap photos of your stack, that would help. We don't even know what size it is. (I assume it is 4") But if there is a hub just above floor level that would be perfect... because then you could insert a donut and pvc into the hub... If not, you will need 2 shielded ferncos.

Assuming there is no hub, just straight cast, from bottom to top, you would need to have: shielded 4" pvc fernco, a short section of 4" pvc pipe, a sanitary tee, another section of 4" pvc pipe, another shielded 4" pvc fernco. You will want the section of pvc pipe you glue up to just fit between the cast, without much play up and down. Loosen and slide both of the ferncos all the way on the cast, with some lube so that they will slide easier. Then insert the pvc that you glued up. Then slide the ferncos halfway onto the pvc and tighten them up.
 
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Old 12-24-20, 06:17 PM
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Pictures included

#1 shows the drain connection into the wall.
#2 same picture but from further
#3 both cabinets side by side shows approx. location of stack



back.
#3 shows the cabinets side by side and approx location of stack.
 
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Old 12-24-20, 07:44 PM
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You would need to remove the sink base cabinet and the lazy susan cabinet in order to connect it to the stack and through the cabinetry.

I assume you are sure that your drain behind the existing sink immediately takes off and goes through the studs to the right, without first dropping lower?
 
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Old 12-25-20, 05:57 AM
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I would definetely check to see if the piping in the wall goes down. It's most common for it to go horizontally over to the stack but you might get lucky.

If your not up to relocating the drain line you can approach it from the other end and not lower the drain. Easiest would be to get a shallower sink. You can also save a little bit of height by converting to 1 1/2" pipe right where you connect to the sinks then you can transition back to 2" at the wall but it will only help if you just need an extra half inch or so.
 
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Old 12-25-20, 06:12 PM
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Goes horizontal over to stack.

Sorry thought I was clear on that, the drain goes horizontal to the stack about 2ft away.
Don't think going with a shallow sink would be best.
I am thinking what XSleeper is saying might be the best overall, rather than dicking around inside the cabinets.
Probably pull the lazy Susan cabinet that would expose the wall where the stack is. Then I can cut out the wall to expose the stack and insert piece of PVC with sanitary tee for connection and fernco connectors. Put the cabinet back in and plumb over to it from the new sink.
Since I will probably have cut out a portion of the horizontal drain out when cutting into the stack for enough room to install new drain connection I will leave the old pipe in the wall. To much work to remove the little left to be worried about it.
It isn't a 4in stack, by looking on the roof looks like 2.5in. Very old house built in 1937. This stack only serves the kitchen sink.

 
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Old 12-26-20, 06:13 AM
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You can run the drain line through the cabinet if you want to try tying in through a hole cut in the back of the lazy susan. I hate doing work like that in a confined space so I'd look hard at removing the cabinets so you can go at it and do a more proper job, especially if the new countertop has not been installed yet. Your vent stack is probably 2" steel pipe so it might be easier to cut than cast iron.
 
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Old 12-26-20, 12:27 PM
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guess I am not getting the whole picture

If removing both cabinets how would I remove the old drain pipe since it will be run through holes in the studs?
I could cut it up in small pieces, but then there would be holes right above where I will need to install the new pipe.
More important how would I install new pipe through the existing studs with out notching?
 
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Old 12-26-20, 12:35 PM
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You don't really need to remove it, you will be tying it below it. You could just put a clean out plug on your existing drain.

If you want to remove it you can, and the old holes make no difference whether they have a pipe in them or not. Your new holes will probably be 4" or so below the old holes.

Your new pipe will need to be installed in 16" sections if you run it through the studs. You drill a hole, insert a short piece of pipe and then add couplers to join those short pieces together.
 
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Old 12-26-20, 12:59 PM
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got it thanks, just seem wrong to put couplings in. But guess don't have a choice.
 
  #12  
Old 12-26-20, 01:12 PM
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Smart Divide Kitchen sink?

This smart divide has anyone used it?
Is it useful?
 
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Old 12-26-20, 01:27 PM
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Divided kitchen sinks are very common. It's a matter of personal taste. Do you want a separate sink to drain things but still have an empty sink for use? If you do dishes by hand it can be a place to set the clean dishes vs the dirty ones.
 
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Old 12-26-20, 03:17 PM
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Threads combined..........................
 
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Old 12-26-20, 06:27 PM
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smart divide comes up 2/3rd of the way
 
 

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