Connect laundry sink drain to washer standpipe?

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Old 11-18-12, 10:36 AM
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Question Connect laundry sink drain to washer standpipe?

I live in Westchester County, New York and want to install a utility sink in my finished laundry room on the first floor of my house. About 24 inches to the left of where I want to install the sink, there is an existing 2" pvc standpipe which the washer drains into, via a u-shaped flexible hose. I have not opened up the wall yet, but I assume near floor level the standpipe is connected to a p-trap and then to a vent/drain. (In the basement below, I can see the 2" drain coming down through the basement ceiling and connecting to the main 4" pvc drain pipe. This 4" pipe runs directly underneath where I will install the sink.) What is the correct way to install the drain for the sink?

I have read several different versions on the web. One source states that the sink can be directly tied to the standpipe (using a wye), at a point above the washer's p-trap, and to not use a second p-trap for the sink. This effectively uses the washer's p-trap and vent for both the washer and sink. Another source says the sink must have it's own trap and vent, which would be a lot more work!

Thanks for any help you can offer!
 
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Old 11-18-12, 05:36 PM
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You definitely don't want to connect to the standpipe. You'll want to plumb it correctly into the drain.

How you connect it depends on how it's set up right now. You may need to add a vent, or you may be able to use the existing one, again, depending on how it is now.

I don't think you can do too much planning until you either open up the wall or figure out what's there now. Can you take some photos?
 
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Old 11-18-12, 07:18 PM
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Yes open the wall and take a pic...

Most likely no!!!! You will need to add a pump to the sink and pipe the pump to the drain...

Its all about venting . The pump allows you to vent properly.
 
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Old 11-19-12, 08:03 AM
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As long as there's no drains above, won't the standpipe serve as a vent? This seems the most obvious plan unless there's some code or reason a standpipe can only be used to drain a washing machine and not a sink.

I'm facing a similar situation where adding a vent to the roof would be difficult and ugly (a log cabin).
 
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Old 11-19-12, 05:49 PM
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Thanks for the feedback. This weekend I'll open up the wall and post some pictures. In the meantime, at the risk of trying your patience, could you tell me what is wrong (if anything) with each of these proposed solutions, and why? I'd like to understand this better.

In case A the sink ties in to the existing drain/vent.
In case B the sink ties in to the standpipe, with its own p-trap.
In case C the sink ties in to the standpipe, without its own p-trap.
In case D the sink ties in to the main drain pipe.

Thanks a lot for your help!
 
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Old 11-19-12, 06:01 PM
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Case A ----- wet vent. Not allowed....
Case B -----same as case A
Case c -----same as case A and B
Case D------ No vent for sink

Here is what you need to do. Case D. Vent sink. Tie in to vent 3 ft above flood plane of sink.
 
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Last edited by lawrosa; 11-20-12 at 06:17 AM. Reason: spelling
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Old 11-20-12, 06:04 AM
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I can't be the only one who doesn't understand. What's a wet vent? IF there was no sink added it would still be wrong?
 
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Old 11-20-12, 06:20 AM
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I'll never understand venting either. I'm not going to argue plumbing code with a plumber, lawrosa but isn't plan C the same as having a double bowl kitchen sink except for the pipe sizes? How about using the existing drain for the new sink and hooking the washer drain hose on the edge of the slop sink? That's how mine is set up.
 
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Old 11-20-12, 06:27 AM
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A wet vent is when a fixture is using a vent. Then you tie another fixture into that vent above it. The space between the two fixtures is a wet vent. Meaning its not always dry.

So you see in case D that I modified the washer vent is dry as well as the sink....

The only other way to do it to use that single vent would be to use a double fixture fitting. But to find one with a 2" side for the washer would be near impossible because I never seen one. It would work with two 1 1/2 discharges though because thats how they make them. Washer needs to be 2"

Shop Mueller Streamline 2" ABS DWV Double Fixture Fitting at Lowes.com
 
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Old 11-20-12, 06:54 AM
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OK I get the wet vent part now--but I really don't see how it could be a problem with a standpipe where there is an INdirect connection to the pipe allowing air in--essentially venting the vent stack.

In any case isn't D the norm with a sink draining directly into a waste pipe with a nearby vent stack? Surely the attachment of the standpipe doesn't mean a 2nd vent is required?

And like toolmon I don't think I'll ever quite understand all the implications of venting. Frankly I always thought a standpipe was intended to BE the vent and an actual outside-vented stack wasn't required on that branch. I've seen just this numerous times--but of course that doesn't make it right Or perhaps it was OK in the past to use a standpipe instead of a vent?
 
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Old 11-20-12, 05:16 PM
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The stand pipe is not a vent. The stand pipe and trap are always tied into a vent.

A vent is used so other fixtures do not siphon water out of the traps.
 
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Old 11-20-12, 07:52 PM
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How does D violate the code? This is the setup in my mothers condo...built in 2004. The SP is right behind the washer. The vent is in the wall right behind that and the slop sink is next to the washer with the drain pipe after the trap dropping through the floor.
 
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Old 11-20-12, 08:21 PM
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In NY travelers drawing the sink has no vent. In my drawing it has a vent. Thats code as I know it.
 
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Old 11-21-12, 08:52 AM
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wouldnt case a be fine if the vent is at least 2" pipe?
Thats how we used to tie stuff up here in CT in all the time doing roughs.
I see where your saying the sink needs its own vent for siphon especially with a w/d and the drain pump force/volume but a 2" vent pipe should suffice no?

On a side note Lawrosa I dont know if you remember/reread my other thread but I completely redid my down stairs drain/vent set up last we talked. I saw the issues you were mentioning and corrected it.
 
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Old 11-21-12, 09:27 AM
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Originally Posted by lawrosa
In NY travelers drawing the sink has no vent. In my drawing it has a vent. Thats code as I know it.
In D (OP version) the sink does have a vent (shared) and as long as it's within the recommended distance from the trap it doesn't need one of its own.


If adding a slop sink to an existing approved system is this complicated I shudder to think what debates will arise when I ask how to vent a kitchen island sink. I think I'll just Google that one
 
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Old 11-21-12, 03:30 PM
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In D (OP version) the sink does have a vent (shared) and as long as it's within the recommended distance from the trap it doesn't need one of its own.
D in the OP version is an "S" trap, and therefore doesn't have a vent. Fixtures can sometimes share vents, but not in a vertical drain like that
 
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Old 11-22-12, 08:24 AM
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Thanks lawrosa for your answers- they are very helpful. Everything you said makes sense, but there are a few details I want to clear up.

1. In your corrected version of Case D, I assume the vent for the sink should be connected to the drain of the sink, downstream of the p-trap, like in the figure I attach here? This is what I plan to do (pending opening up the wall to see what I have!).

2. I read part of the New York plumbing code, and it states that wet venting is allowed, but only if the fixtures are within two bathroom groups. So Case A would be allowed if the washer were a toilet?

3. As toolmon stated, Case C is the way a kitchen double bowl sink is plumbed. Is there a special exception in the code for a kitchen double bowl sink?

4. Continuing from point 3, I understand Case C is not up to code and I don't plan to do it, but I don't understand why it would not be safe. Is the concern that the washer discharge might come out of the sink? Or is there another problem?

Thanks a lot for all of your help. I very much appreciate it. And have a Happy Thanksgiving!
 
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Old 11-22-12, 09:02 AM
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#1...yes
#2...I would have to read it. Wet venting and how its interpreted by non plumbing professional can mean many different things. Like the Bible....LOL
#3... It may be somwhat how a double basin is piped but the vent is still dry. That has nothing to do with your layout.
#4 There are many ways to plumb things. I gave you one way in regards to case D.

Here is another way as in case C or really a modified version. I cant explain in detail about venting and rough plumbing. Its a learned trade. Your best to read a code book and try to understand it but many get overwhelmed and cant grasp it.

Case C
 
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Old 11-22-12, 09:33 AM
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Is there any limit to the number of branches & loops that tie into an existing vent above the ceiling? My attic is unfinished so I can run horizontal vent pipes all over the place and would prefer to do that than have additional roof penetrations.
 
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Old 11-22-12, 09:42 AM
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Yes you can tie into the vent stack in the attic.

As far as how many fixtures can attach to that vent is specific in the code. Its based on size of pipe and units per fixure.

Example, and this is just for reference, a toilet is 4 units, a sink 3 units, tub, 2 units...etc. Equals 9 fixture units. A 3 inch vent stack and support say 15 units.

Then the vent branch, as in our drawings of 2" have a certain unit capacity. As such can usually supply a bath group of a bath, sink and toilet. That vent can terminate through the roof or tie into the main vent.

This is usually not an issue in 1 or two bath homes. Large homes with multi baths will have 2 or three main vents stacks or have the bath groups vent terminate individually through the roof for each bath group.


Thats it in a nut shell.
 
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Old 11-27-12, 06:30 PM
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Here is an update on my project:

I opened up the wall and found three studs ganged together that I would have had to drill through to get to the vent. So I decided instead to add an AAV (which is allowed in New York). I added it under the sink, immediately downstream of the trap, and made sure it stood at least 4 inches above the top of the trap. The drain then goes down through the floor and directly into the horizontal 3 inch drain pipe in the basement. I also made sure I used a wye to connect to the 3 inch drain pipe, and not a sanitary tee on its side, which is what the guy at Home Depot recommended! It all came together in two days, and so far no leaks!

Thanks a lot for all of your help, especially lawrosa.
 
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