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Old 10-17-2016, 01:56 PM   #1
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Drain Size? 1 1/2" for Sink AND DW?


I'm redoing the plumbing in the kitchen. Adding a prep sink and getting rid of the old plumbing for the washing machine that has moved to the back of the house.

Existing sink waste line is 2" iron. Prep sink will tee into the 2" line going to the main line.

If my main sink also has the dish washer going to it, can I still stay 1 1/2"?

Side note....this is what my line looks like under the house.

Looks like it's just lead packing at the joint. I'm thinking, cut the pipe coming up just before the 45...use a Fernco...and ABS the rest of the way.

Side note....I think the 45 is where I've been getting my blockages....I usually have to snake it about ever 18 months.
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Old 10-17-2016, 08:55 PM   #2
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Re: Drain Size? 1 1/2" for Sink AND DW?


Your approach to cutting the cast off is a good idea- but of course, someone will come along and tell you to remove all the cast, but that is your choice...
Use a shielded coupling such as a 2" Proflex CI x PLAS. The neoprene sleeve is sized for the OD's of the 2 pipe types and the band will keep the line rigid- and code compliant.

Per UPC, sinks must be on a minimum 2" line and a dishwasher has no real bearing on the drainage fixture units (DFU) for a kitchen sink.

A sink is either 2DFU or 3DFU's and max loading for a 2" hor. line is 8 DFU so you could put both sinks on the 2" line with room to spare.
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Old 10-24-2016, 03:13 PM   #3
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Re: Drain Size? 1 1/2" for Sink AND DW?


Does the Sanitary Tee have to be 2" at the sink side?

In other words, can I use a 2"x1.5"x1.5"?

Seems silly to have to reduce the 1 1/5" sink drain down to 2"
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Old 10-24-2016, 06:41 PM   #4
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Re: Drain Size? 1 1/2" for Sink AND DW?


Kitchen sinks or prep sinks require 1.5 inch traps and trap arms. So yes, a 2x1.5x1.5 santee.
Vent it 1.5" and add a clean-cut just below the tee, in the vertical 2"

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Old 10-24-2016, 09:41 PM   #5
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Re: Drain Size? 1 1/2" for Sink AND DW?


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Originally Posted by TheEplumber View Post
Kitchen sinks or prep sinks require 1.5 inch traps and trap arms. So yes, a 2x1.5x1.5 santee.
Vent it 1.5" and add a clean-cut just below the tee, in the vertical 2"

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The cleanout goes below the Tee? I would have thought above.

The prep sink is on the opposite wall. The vent is going straight up. No turns.

Do I still have to put in a cleanout? If I have issues, I figure just snake straight down the vent.
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Old 10-24-2016, 09:48 PM   #6
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Re: Drain Size? 1 1/2" for Sink AND DW?


Common practice is clean out below, but it makes little difference. I've seen them plumbed to the exterior before too- rather than inside a cabinet...
UPC requires them on sinks regardless of vent access or length of drain branch. I believe LA is variant of UPC.
It should be 2" too so if you go above the tee then it changes your tee size and you would add a bushing on top to reduce for the vent.
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Old 10-28-2016, 03:00 PM   #7
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Re: Drain Size? 1 1/2" for Sink AND DW?


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Common practice is clean out below, but it makes little difference. I've seen them plumbed to the exterior before too- rather than inside a cabinet...
UPC requires them on sinks regardless of vent access or length of drain branch. I believe LA is variant of UPC.
It should be 2" too so if you go above the tee then it changes your tee size and you would add a bushing on top to reduce for the vent.
I pulled my permits on Tuesday and had a chat with the inspector.

I said below.

On the one sharing an outside wall, I 'was' going to have the access from the outside....but I think I'll just do it inside. It's a lot easier to cut a hole in drywall than cut ledger stone around a cleanout.

One question....

He also said it was ok on my San-T to have the sink side 1 1/2".

Any reason I can't use a threaded coupling there? That way, should I ever have to replace the drain and the stub out is not long enough, I just unscrew and replace with a new one. Not worried about the cost of parts....$3 total in parts?
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Old 10-28-2016, 03:30 PM   #8
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Re: Drain Size? 1 1/2" for Sink AND DW?


And one more question.....

The attached 'chicken scratch' drawing is the layout under my kitchen.

Top part is the view looking down.

The short leg on the right is my existing sink...the longer leg on the left is the new leg to the prep sink.

I see two options on running the prep sink line...

1. Adjust the angle so the pipe runs straight to the Y

2. Go shallow angle on the pipe and mount the Y side vert so the water drops into the Y

Part of my problem....if I do the straight shot, I block the crawl space and make it harder to get around the pipe....AND...the angle is such, I would have to modify or piece together turns to get the angle.

How would you tie in the prep sink leg?
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Drain Size? 1 1/2" for Sink AND DW?-kitchen-drains.jpg  
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Old 10-29-2016, 10:49 AM   #9
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Re: Drain Size? 1 1/2" for Sink AND DW?


Quote:
Originally Posted by ddawg16 View Post
I pulled my permits on Tuesday and had a chat with the inspector.

I said below.

On the one sharing an outside wall, I 'was' going to have the access from the outside....but I think I'll just do it inside. It's a lot easier to cut a hole in drywall than cut ledger stone around a cleanout.

One question....

He also said it was ok on my San-T to have the sink side 1 1/2".

Any reason I can't use a threaded coupling there? That way, should I ever have to replace the drain and the stub out is not long enough, I just unscrew and replace with a new one. Not worried about the cost of parts....$3 total in parts?
Why add threads and create a possible leak point?
If you come up short in a future remodel, cut the pipe and glue on a coupling to extend it. That's the advantage of solvent weld joints 😉

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Old 10-29-2016, 10:57 AM   #10
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Re: Drain Size? 1 1/2" for Sink AND DW?


Quote:
Originally Posted by ddawg16 View Post
And one more question.....

The attached 'chicken scratch' drawing is the layout under my kitchen.

Top part is the view looking down.

The short leg on the right is my existing sink...the longer leg on the left is the new leg to the prep sink.

I see two options on running the prep sink line...

1. Adjust the angle so the pipe runs straight to the Y

2. Go shallow angle on the pipe and mount the Y side vert so the water drops into the Y

Part of my problem....if I do the straight shot, I block the crawl space and make it harder to get around the pipe....AND...the angle is such, I would have to modify or piece together turns to get the angle.

How would you tie in the prep sink leg?
I would use a combination wye/45 rolled up at a 45 from horizontal.
Start at your sink and run your drain as high as possible, then use a 45 to drop down to the combo I mentioned first.
Hopefully you could then crawl under...

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Old 10-30-2016, 03:33 AM   #11
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Re: Drain Size? 1 1/2" for Sink AND DW?


Thanks E.....

I picked up a bunch more 'parts' today...and what you describe is what I concluded to be the best way to go.

Thanks for confirming.
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