Moving a vanity drain about 4 feet

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rpdwyer

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Hi all.

I have a drain pipe (1-7/8” OD) I need to move about 4 feet for a new sink we will be installing (this room was rough plumbed about 16 years ago and we are only getting to finishing it now)

In the attached drawing the drains current location is in red hash and marked as “drain/vent”. It connects to a larger pipe in black hash labeled “main vent” that it uses as its vent.

What I need to do is move that drain about 4 feet to the location marked “new drain location” at the end of the blue dotted line representing the run. This new location will be within a new 2x4 wall (not yet framed).

Is this procedure as simple as cutting out the existing T that serves as the current drain location and attaching a new T several inches below it off of which I run my new length of drain tube (represented by the blue line) to the new location?…or do I have to also have a vent run up the wall from the new drain location and tap back into the main vent?

Thanks for any info.

—Rick
 

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jadnashua

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If your drawing is showing expected routing, how would the waste go uphill to get to the existing drain?

Two other issues:
- a 1.5" ID drain must be vented in a shorter distance than you show. Don't remember on 1.5" pipe, but for 2", it must be vented within 5', and gets shorter with smaller pipe.
- you can't use the vent line from the existing location because it is too far away, but if you cut that connection out and ran it towards the new location, you can. It must be at least 42" above the floor, or 6" above the flood plane of whatever is draining in that room, whichever is higher.
 

Terry

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Grading it at 1/4" per foot, you can be within 42" of the p-trap, and have 135 degrees of change.
It looks to me that you will be adding a vent in that new wall.
 

rpdwyer

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So if I understand it correctly, my new run should look like the black line I depict in the attached screenshot?
 

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MACPLUMB

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Cut a tee into the main stack and run from there instead of trying to hop scotch around the main stack,
 

rpdwyer

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Wasn't sure I could do that because it's not clear to me what that main stack connects to on the floor below me. So in my drawing it's clearly a vent as it goes up and out to the roof. However, if that stack somewhere below me acts as a drain for the sink or shower in the room below does that cause a problem?

--Rick
 

Cwhyu2

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Wasn't sure I could do that because it's not clear to me what that main stack connects to on the floor below me. So in my drawing it's clearly a vent as it goes up and out to the roof. However, if that stack somewhere below me acts as a drain for the sink or shower in the room below does that cause a problem?

--Rick
Yes it does and I would try to connect to the original drain.
 

Jadziedzic

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Note Terry's comment re: 135 degrees of directional change in the drain line; more than that (as in your diagram) and you'll need an accessible cleanout.
 
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rpdwyer-Moving_a_vanity_drain_about_4_feet.jpg

I believe this is what you are trying to do with your diagram. It may contain assumption errors, since you did not provide any actual photos.

There are pros to not having to tamper with the big main stack. It won't be very flexible, or not at all, any joins made back to it will need couplers. Banded couplers are great for those cornered into a rock, but if a pipe can be left one piece, I prefer to do that.

That means cutting into the smaller existing drain, and that would probably be flexible enough to avoid any couplers, you'd be doing it all with tees wyes whatever.

If you go with that Terry said about a wet vent, then all you need to do it install the blue part of the diagram. That's graded slightly as he explained it. Try that, and if your trap siphons out, go ahead and install the purple part of the diagram for the vent.
 

jadnashua

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Assuming the horizontal vent line from the existing location was done to code, you CANNOT run the vent from the new location lower. It MUST go up to at least 42" above the floor OR 6" above the flood plane of the highest fixture in that room, whichever is higher, before it can run horizontally. And, the horizontal section MUST have slope down at a minimum of at least 1/4"/foot so any condensation or melt water can drain out and not block the vent.

You CANNOT use a vent line from below for your drain without making other changes. With few exceptions, once a drain, always a drain and the same applies to a vent.
 
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