Double Bathroom sinks

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Mark Polman

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Remodeling a second floor bathroom and I was planning on adding a second sink. Our original layout only had one, and my wife does not want to share anymore. I opened the wall to take a look, and here's what I have (see picture attached). Can I tie the second sink into the existing drain by extending it to the left, which would leave the second sink around 6 feet from the vent (behind toilet), and the original placement of the sink will move a little closer to the toilet at around 3 1/2 feet. I what I've read, the distance from the vent to a sink's p-trap for a 1 1/2 diameter drain pipe is 3 1/2 feet. So, I'm assuming that the answer to my question is 'no'. But, I was watching a YouTube video (screenshot attached) where they were installing water lines with a layout similar to my own and their drains looked farther than 3 1/2 feet. Their drain looked larger than 1 1/2, so if it's 2 inch, it still looks farther than 5 feet from the vent. What are my options here? My search for distances from the trap to the vent have been all over the place as well, so what are the distance for 1 1/2 and 2 inch drains from the vent?

Thank you,

Mark
 

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breplum

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The YouTube image is what we expect from the internet. That image has so much wrong that I won't begin to waste my time.
The distance allowed by UPC for trap arms to a vent is 3' 6" for 1-1/2" pipe.
IKEA has many double sink tubular set-ups for their cheap/nice? style of vanities with double sinks. NOT code, but it would work. Just don't ask an inspector to approve it, nor would a decent home inspection upon sale necessarily think it was ok.
My opinion is, if you have the modern super low flow lav faucets, there is so little loading during use that the 1-1/2" should work.
BTW, the allowed trap arm distance for 2" pipe is 5' to the vent
 

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Thank you breplum for the info. If I wanted to follow code, since the second sink will be 6' from the vent directly behind the toilet, I would then need to add a vent between the second (left sink) and the first (right sink), (see attached drawing) correct? And you don't feel that I need to change the 1 1/2" drain to a 2" drain, that the low flow of the two sinks will be handled without issue with the 1 1/2" drain pipe? I don't have a problem changing it to 2", what would you do if it was your house?

Thank you so much for the advise, I appreciate the time you all take to help others!!
 

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breplum

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Basically yes, creating a new vent off as pictured is a way to do it. Though not to code.
When I get a chance I will send a sketch. no time now.
If you want to do a conventional double lav as described, if it were my house, I would do the 2". It will give many lifetimes of no-grief flow.
Over time with build up of crud, the 1-1/2" will be sooner to need snaking.
 

breplum

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Long sweeps required on the ends of the lav branches. Put a clean out under the fig. 5. 62D87EE2-F5D7-45AC-AA97-9145582F33A2.jpeg
the clean out fitting: 2” “test tee” aka clean out tee.
 

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Thank you for tall the advice, I really appreciate it.

I had another thought that I wanted to run by you as far as configuring the new double sinks. I have an old bathtub drain line that runs across the floor from where the bathtub used to sit and runs almost right under the position where the second sink would be installed. The 1 1/2" line was plugged off since it wasn't used when the bathtub and shower switched positions. The plumber tied both the tub and shower into the old shower drain, thus eliminating the old tub drain line. Would it make more sense to tie the second sink into that old drain and then run a vent as I outlined in diagram 6 (attached)? My only thought was that each sink would then have it's own drain, and it's already there. So I would leave the existing plumbing for the sink on the right, moving it to the right slightly which would leave it in within the 3'6" distance from the vent behind the toilet, then tie the second sink (one on the left) into the old 1 1/2" drain that the tub used to use and connect the vent as shown. The old vent for the old bathtub drain was across the room near where the tub used to sit. To be clear, the old bathtub drain runs across the floor, past the wall where the new sink would sit, continuing on for a foot or so before tying into the drain line that runs perpendicular to it and finally dropping down into the basement. So, I could eliminate the old drain section that runs under the bathroom floor and start the connection at the new sink location, where it would just tie in to the drain as it does now. Thoughts?
 

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breplum

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Certainly from your description it should be fine and an approved use of an existing (unused) drain.
What type of material is that old tub drain? If it is old 1-1/2" galvanized, then I would generally avoid it because old galv. is junk.
You may want to snake out whatever it is before connecting, as insurance.
And water blast test the old drain as well.
Cleanouts are, by code, not required above first floors. But, never hurts having one. Esp. with today's low flow fixtures, there is bound to be increasing build up greater than the old days of higher flow fixtures.
 

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The old tub drain is 1 1/2 abs, it's the same age as all the plumbing in the bathroom. It was in use up until a month or so ago when we remodeled the other side of the bathroom, moving the tub where the shower used to be and the shower where the tub used to be. So, no worries of the old tub drain leaking, as it had been flowing without any leaks. If it were your house which way would you configure the two sinks, figure 5 or figure 6? As far as the clean outs, how would I access them? Leave them accessible with a hole in the drywall and back of the cabinets?
 

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I would go ahead and use the old tub drain.
ABS is required to be supported, rigidly every four feet, because it can bow up and down if not supported ridgidly.
Cleanouts are left accessable with a cut out in the drywall/cabinetry.
For a really spiffy pro job, we use countersunk ABS plug that has a brass 1/4 -20 tapped inset (we find them at local ACE hardware stores more often than supply houses) and then use plumbing cleanout covers (typically stainless steel).
 

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The vertical vent height just needs to be higher than the over flow height of the sink before it turns horizontal, correct? I was planning on making the turn towards the main vent behind the toilet at about 5 1/2 feet above the sink's trap, well above the sink over flow. There isn't any minimum venting code other than that minimum is there?

I have a local ACE hardware near me, I will take a look.

Thank you for all the advice and help!!! I really appreciate it!
 

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Code for horizontal venting 6" above the overflow height of the countertop. Exceptions are allowed -generally- for lower, if long sweep 90 fittings are used.
Basically, they don't want the vent filling with crud in the case of a bad backup and then subsequently, not fully washing away.
 
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