Double vanity drain questions

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Vinmassaro

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I am converting a single vanity to a double in my bathroom renovation. I redid it and after looking at pictures online, think it may be wrong. I used Proflex shielded couplings to tie into the existing 1-1/2 copper drain and used a double wye with street 45s and non-sweep elbows. Please let me know if this is incorrect and should be redone. Thank you.

IMG_2873.jpg
 

wwhitney

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Yes, it should be a double fixture fitting, not a double wye.

For the lav traps to be vented properly, the following has to be true (sort of backwards from the usual presentation of the trap weir rule): suppose the traps are dry and you stop up the vertical drain below your double wye, and slowly added water from the bottom. At some point the water will reach the crook of the double wye, causing the top (vent) opening to become a separate air space from the side entries. At that point, water must have already risen into the trap arms and spilled in the trap.

Also, the 1-1/2" copper above needs to be a dry vent, no drainage coming down from a story above.

Cheers, Wayne
 

Vinmassaro

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Thanks, I will switch this to use a double fixture fitting. What I've read is that 2" PVC should be used for a double sink, but my drain is only 1-1/2". In this case should I be using 2" from the sinks and reduce down to 1-1/2" at the double fixture fitting, or does it not matter?

I see the double fixture fittings come in either, these sizes, which should I use?
- 2"
- 2" x 1-1/2" x 1-1/2" x 1-1/2"
- 2" x 2" x 1-1/2" x 1-1/2"
 

wwhitney

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With only a 1-1/2" drain, you will need to use a double san-tee rather than a double fixture fitting. The IPC is OK with two lavs on a 1-1/2" drain. A cleanout below the double san-tee may be appropriate, as I understand it can be hard to snake through a double san-tee and come out the bottom rather than the opposite side (no personal experience).

Other options, in case one is helpful: you could stack two san-tees, and the two lav drain stubouts would end up at different heights. Or you could split the stack, with a wye above and below a san-tee for the right side drain, and a short vertical segment for a san-tee for the left side drain.

Cheers, Wayne
 

Terry

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When you only have 1.5" pipe coming up, I do this.

single_to_double_lav.jpg


Current UPC plumbing code wants 2" at the bottom, but sometimes it's an older home that only had 1.5", so this is the best that I can do. Wayne mentions that IPC is okay with 1.5"

Also very easy to snake latter as a double 1.5" santee is nearly impossible to snake later.
 
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Vinmassaro

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When you only have 1.5" pipe coming up, I do this.

single_to_double_lav.jpg


Current UPC plumbing code wants 2" at the bottom, but sometimes it's an older home that only had 1.5", so this is the best that I can do. Wayne mentions that IPC is okay with 1.5"

Also very easy to snake latter as a double 1.5" santee is nearly impossible to snake later.
Thanks for that photo. It looks like I could do make that work even with the limited space I have with the close stud. Is there any minimum distance above the sanitary tees before tying back into the vent? Your photo has it up high but just wanted to double check.
 

wwhitney

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Yes, allowed if you use a LT90 with it (I can't tell from the picture whether it's a quarter bend or LT90).

But if you are going with Terry's picture, why are you putting the secondary vertical drain/vent on the right of the the existing? You have a lot more room on the left. Including for a wye/45 instead of a san-tee/LT90.

Cheers, Wayne
 

Vinmassaro

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Yes, allowed if you use a LT90 with it (I can't tell from the picture whether it's a quarter bend or LT90).

But if you are going with Terry's picture, why are you putting the secondary vertical drain/vent on the right of the the existing? You have a lot more room on the left. Including for a wye/45 instead of a san-tee/LT90.

Cheers, Wayne
Good point, I was looking at it too literally. I’ll just reverse it. Thanks!
 
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