Plumbing Double Sinks
 

A newbie plumbing question.

Designing a double vanity. Want to sacrifice as little volume to the plumbing as possible. Can you connect both sinks with horizontal pipes into a wye then to a single, shared P-trap?

I’m going to say no, as I’ve never seen that set up before. Each sink has their own p trap and it’s tied into a single waste line in the wall.

Yes you can. ( not necessarily with a wie, but a sanitary tee...)Normal configuration by code. Thats how i always do it.

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You can but, more chance of odor from the drain and the horizontal pipe with the P trap being far away.

I think its actual legal here too but we never do that. We always have separate p-traps for each sink and make connection with a long radius Tee way down below or behind the wall into the waste pipe

The other reason is noise. You will hear water draining from the other sink. No good

Double p- traps are against code here in NJ

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Don’t think he’s referring to double trap on a single fixture (against code here as well AFAIK).

I just went through this design work myself. The sinks can be installed with a single p-trap as long as they are within 30” of each other. When I laid it out, I preferred separate p-traps into the wall, down through the floor into the crawl space where I teed them together.

In the event of having to work on leaks in the vanity, I liked the idea of not affecting both sinks at the same time. Also, the plumbing took up more space with a T layout before the trap YMMV.

This, like I mentioned earlier, better work too. Unless its a slab, then connection should be behind the wall.

John, you have come this far, it isn't worth the small amount of trouble of opening up drywall and patching. GEt it done correctly.

I was not thinking of avoiding in-wall work. I am more thinking about maximizing the usable volume inside the vanity for drawers etc. Like, maybe I could have a single P trap in the center of the vanity, between the sinks, and thus have a full stack of drawers beneath each sink.

We’ve decided to replace our always-irritating single pedestal sink with a double vanity. There is 66” of width available. We looked at various double vanities, the <$1,000 ones were press-board and the actually-wood ones were $3,000++. So I’m thinking of two more options: i) find a super cool old dresser, something with a bombe front or etc, and convert it, or ii) have a double vanity custom-made to measure. Either way, if we’re going to spend money on this, I want maximum storage. The bathroom is small :-(

If you are doing all that, I have a solution for you but it will require some mods to the dresser drawers. I am just about to go to work now, but will get back to you later this evening.

One P-trap one sink.

I'm assuming what you're hoping for is "her sink" and "your sink".
You're not going to get that.

What I currently have is "her sink", surrounded by so many bottles of potions and elixirs that there's no way I could use it without knocking half the stuff onto the floor.
The other sink contains a makeup bag, an open giant container of Q-Tips, and both a curling wand and a hair straightener, rendering it completely unusable.

Just add more drawers. Don't expect access to any of them.

Wash your hands in the kitchen sink, or use the hose outside.

I did that (drawers under sinks) Each sink got a std trap, and I made rough was centered on each sink. Kept traps high with vessel sinks, and they just needed a narrow notch in each upper drawer.

Actually, one sink will be “hers” (wife) and the other will also be “hers” (daughter). I’ve already been pushed out to the half-bath on the ground floor, and am periodically chastised for having my stuff in view of the guests who might be offended by the sight of it.

Oregon Plumbing Code permits two sinks on one trap, with conditions

"One trap shall be permitted to serve a set of not more than three single compartment sinks or laundry tubs of the same depth or three lavatories immediately adjacent to each other and in the same room where the waste outlets are not more than 30 inches (762 mm) apart, and the trap is centrally located where three compartments are installed."

I’m pretty sure we’ve discussed this before.

In our kitchen, I installed 2 p traps for the double sink. Code allows for 1 or 2. Our dishwasher discharge ties in between them and the dishwasher hose acts as a p trap in itself.

We don’t hear any burbling when we drain one sink, neither has ever plugged, it works great.

I’m surprised any jurisdictions would not allow for one trap per sink… I suspect that like many Canadian codes, the wording allows for one trap for both sides and people read it as must be only one trap for both sides of the double sink.

As I suspected from the NJ plumbing code of 2021…

One trap for a multi compartment sink is allowed… (exception 3) but it is a ‘May’ not a ‘shall’. This means you can do one trap per sink compartment or one trap for both.

What is NOT allowed is putting 2 traps in series (one after another) without a vent between them (5.1c).

http://forums.pelicanparts.com/uploa...1724839470.png

Read the code in your jurisdiction, be mindful of the ‘shalls’, ‘Mays’, and ‘musts’…

See my post above…

Completely aware of "may"and "shall". Been a contractor for over 30 years.
I speak on experience with dealing with numerous jurisdictions and their requirements. I've done tens of kitchens, baths. Residential and commercial.
Just saying what I run into.

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That screen capture is the NJ code. Double p-traps are NOT against code in NJ (unless you meant connecting 2 traps in series).

That is what I'm talking about. Because one will draw the water out of the other.

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^^^ you bet.

If I use vessel sinks this would be less of an issue. The P-traps would still take up volume in the vanity, but the sinks would not. I'm not sure I want vessel sinks.

Another option is to have custom sinks with the drain at the rear edge of the sink. The P-traps could then be along the back of the vanity (the "P" in a plane parallel to the wall) leaving most of the vanity depth for drawers. However, from my experience with custom SS kitchen sinks, I suspect a pair of custom SS vanity sinks will cost at least $2,000.

If you get an old dresser, keep the fronts and make a set of new drawers but at least 3 inches shorter in depth (not height). On the top drawer a notch may have to be cut to allow the tail pipe to clear. As soon as the tail pipe comes out from under the sink, connect a 45 and turn that pipe to the back of the cabinet where you have the 3" gap from the shorter drawer. INstall the p trap there, and connect to the drain behind the wall. Works perfectly each and every time. Basically the drain lines are in the back of the cabinets and not right under the sinks. You are attaching that to the wall? Another trick is to have a plug attached to the back of the drawer so a blow dryer is always plugged and goes back into the drawer when not in use to save counter space. To make it legal, use a pig tail from drawer and plug into an existing socket that will be installed in the area behind the drawer. It becomes a plug in item.

If any of you are wondering about the angle, it there to clear the sink.

look 171, is the plug in a drawer legal in CA? I understand you are bending the rule by plugging it in, quite sure unless the circuit turns off with drawer closed and has a heat sensor it would not be legal here.

JYI if you are tall you will like vessel sinks, get that added couple of inches in height.

Legal. but need to be GFCI but that's behind the wall. I have done it for years and have never had any issues during rough inspection. By final they never question or even noticed. Perfectly legal to have a plug inside the cabinet. Same circuit as the sink plug on a dedicated breaker.