Dropping sink drain for new deeper sink

[Gifty74]

Typical situation; installed new granite, went with a deeper under mount SS sink and the waste line of the disposal is about 1/2” lower than the drain where it exits into the wall. Want to drop the drain line about 2”, and seems very easy to just punch a hole through the floor of the cabinet under the sink and connect into the existing line that currently heads horizontal through 3 studs and then down through the subfloor. Question is, is there any reason I can’t just drop straight down through the floor under the sink and T into the line that I can see from the current setup? Why would the builder or plumber at the time go out through the wall under the sink, through 3 studs, then down and bend back horizontal to head the length of the house to the main drain exit? Why wouldn’t they just do it how I am planning to? Is there a code or other reason it wouldn’t work to go straight down and keep it on the same pitch as the main run down the length of the house?

 

[Jadnashua]

It may be possible, but the vent MUST occur after the trap and before the drain line goes down. If your locale allows it, you might be able to use an AAV, but a real atmospheric vent is always the better choice when available.

 

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[Gifty74]

After some further investigation it looks like drilling the exterior studs and lowering the drain line is going to be a pretty big PITA. The DWV tee is right behind the cabinet that is adjacent to the opening under the sink (corner sink location, far corner of house). The cabinet where the tee is behind has studs blocking both sides to get access to it (from under the sink side, and range on other side). Really does not seem to be a great option unless I open up the wall from outside the house, and really don't want to get into that. Only feasible option seems to be to go down through the floor, and horizontal to tee into the existing line that is on the far joist in the basement, which would be after the vent. If I teed in and kept the existing line (that is just below the DWV pipe, but would tee in horizontal to it) would it still vent back up and out the existing line?

 

[Reach4]

Why would the builder or plumber at the time go out through the wall under the sink,

Because going through the floor of the cabinet under the sink takes up storage room under the sink and looks a bit hokey. Plus, you need a vent anyway, and a proper vent would pass through the walls rather than emerging above the counter.

, through 3 studs, then down and bend back horizontal to head the length of the house to the main drain exit?

Separate question. I did not follow your path descriptions, although I did not work at it. One possibility is the pipe that you are looking to pass waste into is a vent rather than a drain.

 

[Terry]

A vent needs to be higher than the trap arm for the p-trap to prevent siphoning of the trap.

It used to be that a deep sink was 8". Now kitchen sinks are often 10" deep, meaning that there are plenty of roughed in sinks that won't drain the disposers fully when the kitchen counters are redone with an undermount 10" deep sink. I've changed my standard rough-in to 16" off the floor now for that reason.

 

[Gifty74]

Thanks Terry, got it. I've attached a picture to explain a little better. Hatching is all open area under sink. To right side of studs is exterior. DWV position is theorized although looking outside at the roof line there is no vent through the roof anywhere near this theorized location. Drain pipe runs through 3 studs, then drops down through floor where I can see it in basement, and jogs over 12" or so and runs the rest of the length of the house down the joist.

What I'm looking to do is drop straight down through the floor under the sink, in the back side, and tee into this line. It's kind of tight where I can access is as it's the last joist before the block wall in the basement so I only have about three fourths of the joist opening to work in to try and tee this into.

 

[Terry]

It looks like you can add a wye to that to get over to the sink.

 

[Gifty74]

Ok. And what is the trick for ‘sweating’ a wye or tee in there when both sides are rigid / attached?

 

[Ladiesman217]

Will a different garbage disposal make a difference?

6" drain specification, but says to add ½" for stainless sink

https://www.insinkerator.com/resour...&languageCode=en&countryCode=US&type=document


Can you change out the sink to a shallower version?

 

[Gifty74]

Nope. Evolution Compact same waste outlet height as my current Insinkerator Badger.

 

[Ladiesman217]

Nope. Evolution Compact same waste outlet height as my current Insinkerator Badger.

Too bad.

Can you replace the sink with a shallower sink? The countertop opening would have to match, so that may not be practical.

Is that a double sink?

How about a picture of the under counter sink area plumbing. Maybe a picture of the counter and sink topside.

 

[Gifty74]

Sure, pics of both attached. Yes, a shallower sink was considered, but this one has some scratches now so returning to Wayfair might be an issue, and getting a new one to match...all of that, seems like the new drain is the best option.

 

[Ladiesman217]

Nice!

So to be clear. When you measure the distance from the cabinet floor, the center of the y drain pipe opening is two inches higher than the center of the garbage disposer drain opening?

My kitchen sink vent pipe is located just above the drain pipe entrance inside the wall. How are you going to vent the new drain pipe?

 

[Reach4]

So to be clear. When you measure the distance from the cabinet floor, the center of the drain pipe opening is two inches higher than the center of the garbage disposer drain opening?

I think he was saying the left ends of the orange and yellow lines are 1/2 inch higher than the right ends.

This would have been a good place for one of those sinks with a shallower disposal side.

 

[Gifty74]

Yes, correct. Garbage disposal waste about 1/2" lower than entrance of the drain pipe into the wall (the highest point). And for sure, an 8" sink would've solved it (this one is 10"), or a shallower disposal side. Monday morning quarterbacking with that though, the counters are in and so is the sink. Guess I'll use some repair / existing PVC couplers and try to get enough room under the joist to finagle in a wye. I would think because I'm joining into the existing line that is dropping down through the floor in that earlier pic, that it will vent there. I'm going to put a vertical stack on the new drain line I'm putting in, 6" up, and cap it. If it's not draining well I will put on a mechanical vent under the sink.

 

[Reach4]

Mechanical vents don't help draining. Vents prevent gases from coming into the living space by preventing the traps from siphoning out.

You could keep the current drain for the left bowl, and run the new drain, with trap and AAV, through the floor.

 

[Jadnashua]

One easy and code compliant way to add a section of pipe in when you can't spread it apart is to use banded couplings. These are a rubber sleeve with metal reinforcement around them. You could also use a repair coupling, but those can be a pain to get on before the cement sets up. A repair coupling doesn't have a center stop, so you slide it one way, then try to slide it back before the cement grips so that it is then centered over the joint. A banded coupling is much easier but more expensive.

 

[Ladiesman217]

Yes, correct. Garbage disposal waste about 1/2" lower than entrance of the drain pipe into the wall (the highest point). And for sure, an 8" sink would've solved it (this one is 10"), or a shallower disposal side. Monday morning quarterbacking with that though, the counters are in and so is the sink. Guess I'll use some repair / existing PVC couplers and try to get enough room under the joist to finagle in a wye. I would think because I'm joining into the existing line that is dropping down through the floor in that earlier pic, that it will vent there. I'm going to put a vertical stack on the new drain line I'm putting in, 6" up, and cap it. If it's not draining well I will put on a mechanical vent under the sink.

If you run a new drain line, you can use the existing drain line as your kitchen sink p trap vent connection. Your present drain is vented, and it will be dry after you make a new drain pipe connection. No AAV would be required.

 

[Gifty74]

I was right there with you a few days ago, but after looking at how simple it is to drop down through the floor vs. trying to match up a new shallower sink, most likely losing the $275 for the current one, etc...re-routing the plumbing seems like the way to go. Here is how I'm envisioning this... and actually see there's a 1.5" to 2" 90 elbow so no coupler needed, just a short piece of 1.5" to mate up with P trap.

 

[Gifty74]

If you run a new drain line, you can use the existing drain line as your kitchen sink p trap vent connection. Your present drain is vented, and it will be dry after you make a new drain pipe connection. No AAV would be required.

Ok, so how would this be laid out. Can you sketch?