Washing machine drain piping into stack

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SS396

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, Hello. The attached picture shows how a 2 inch drain line from my laundry area turns down 16 inches or so down into the wall cavity and into the wye connection on the 3 inch stack. I am hoping to remove the wall and enclose the stack within a column. I only want to enclose the 3 inch stack and pressure lines to keep the column as small around as possible. Therefore, I would like the washer drain line to enter the stack in the ceiling area, not in the wall cavity. The vent pipe on the far right is only for the kitchen sink and it will be replace with an air admittance valve. That will leave only the 3 inch stack and the pressure lines to be enclosed within a column. I am asking if the existing 3 inch 90 deg elbow from the toilet could be replaced with a double 90 elbow so that the 2 inch washing machine line drains into one side (with a bushing), and the toilet drains into the other opposite side of that proposed double. Or is there some other suggestion? Thanks
IMG_E6973 (2).JPG
 

wwhitney

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Is minimizing the column that critical for your design? Because DWV-wise there's an upside to keeping the atmospheric vent, and you could move the vent to nestle in between the 3" and 2" drains for a more compact column (still bigger than what you propose).

I have heard that double quarter bends are in disfavor because when snaking you may cross over rather than end up downstream. Otherwise, a double quarter bend would work for you.

An unusual choice would be a 3" san-tee with 2" sanitary side inlet, where you plug the top entry. That would presumably address the snaking issue, but would introduce another LT90 on the 2" drain.

Cheers, Wayne
 

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Thank you Wayne, Regarding the vent, there are other issues as well. The sink installs on the adjoining peninsula wall and the horizontal section of that vent is above the flood rim as required. We don't want that raised bar look and we want the entire surface of the countertop to be one flat surface at a normal 36 inch height. I am thinking a Studor vent under the sink, which I guess would make all of that vent piping superfluous. I would certainly welcome any other ideas.
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wwhitney

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I'm not necessarily advising against an AAV, they have their uses, I'm just trying to give you the alternatives for an atmospheric vent.

For a sink set into a countertop that abuts your column, with no framing above the countertop height other than the column, you can still make that work if the sink is close enough to the column, and you are flexible on where the drain penetrates the floor. The trap arm is the horizontal pipe from the trap outlet to the vent connection; for a sink that vent connection is typically a san-tee where the drain also turns downwards. Under the IPC (which I believe you are subject to), a 1-1/2" trap arm can fall up to 1-1/2" total and be up to 6' long (which requires a perfect 1/4" per foot slope, the minimum allowed).

So if you can put your san-tee in the column, and run your trap arm under the counter and popout into the sink base and hit the trap with a total length of 6' or less, it can work. It's best not to have two many elbows in the trap arm, but a single LT90 or two 45s would be fine.

The more complicated option is to put the san-tee next to the column but not within it. Then the dry vent is allowed to be up to 45 degrees off plumb and still be considered vertical. So at the top of the san-tee you could have a street 45 to start moving towards the column as the vent rises. If the vent can make it into the column before it comes out the top of the cabinet, that would also work. That could give you an extra foot (or more) of horizontal distance between the column and the sink, or it could eliminate some elbow(s) in the trap arm.

Cheers, Wayne
 

SS396

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I'm not necessarily advising against an AAV, they have their uses, I'm just trying to give you the alternatives for an atmospheric vent.

For a sink set into a countertop that abuts your column, with no framing above the countertop height other than the column, you can still make that work if the sink is close enough to the column, and you are flexible on where the drain penetrates the floor. The trap arm is the horizontal pipe from the trap outlet to the vent connection; for a sink that vent connection is typically a san-tee where the drain also turns downwards. Under the IPC (which I believe you are subject to), a 1-1/2" trap arm can fall up to 1-1/2" total and be up to 6' long (which requires a perfect 1/4" per foot slope, the minimum allowed).

So if you can put your san-tee in the column, and run your trap arm under the counter and popout into the sink base and hit the trap with a total length of 6' or less, it can work. It's best not to have two many elbows in the trap arm, but a single LT90 or two 45s would be fine.

The more complicated option is to put the san-tee next to the column but not within it. Then the dry vent is allowed to be up to 45 degrees off plumb and still be considered vertical. So at the top of the san-tee you could have a street 45 to start moving towards the column as the vent rises. If the vent can make it into the column before it comes out the top of the cabinet, that would also work. That could give you an extra foot (or more) of horizontal distance between the column and the sink, or it could eliminate some elbow(s) in the trap arm.

Cheers, Wayne
Thank you Wayne for those suggestions on the venting. The span is just too long for the 45 deg vent to work. As for the other, I was wondering myself if there was some way to abandon the separate floor entry for the kitchen sink drain and utilize the 3 inch in the column but I'm not sure that is what you mean?? By the way, I picked a 3 inch santee with 2 inch side inlet for the washer drain connection and that looks like the way to go for the washing machine drain. I think that will work better than the double 1/4 elbow. So the santee replacing the existing 90 deg elbow with the toilet running into it and the washer line into the 2 inch side entry and the top 3 inch entry capped would be an unusual usage of that fitting but would likely pass inspection?
 

wwhitney

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Thank you Wayne for those suggestions on the venting. The span is just too long for the 45 deg vent to work.
That was meant as something to do in addition to moving the kitchen sink san-tee, if you need a little extra distance.

As for the other, I was wondering myself if there was some way to abandon the separate floor entry for the kitchen sink drain and utilize the 3 inch in the column but I'm not sure that is what you mean??
Sure, you could do that if the san-tee ends up close enough to the column.

By the way, I picked a 3 inch santee with 2 inch side inlet for the washer drain connection and that looks like the way to go for the washing machine drain. I think that will work better than the double 1/4 elbow. So the santee replacing the existing 90 deg elbow with the toilet running into it and the washer line into the 2 inch side entry and the top 3 inch entry capped would be an unusual usage of that fitting but would likely pass inspection?
I'll say yes, and it should. I can't say what inspector will do, but I'm not aware of any rules it would violate. If the fitting didn't have the top entry, it would be what you want, so just plug the top entry; at least that's my thinking.

Cheers, Wayne
 
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SS396

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Wayne, Just to be sure, is this the alternative layout for the sink drain that you were speaking of?
 

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wwhitney

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Yes, that's the idea. It would be nice to avoid having two LT90s on the trap arm (180 degrees of bend), that would require a trap arm cleanout, IIRC. 90 degrees of bend would be OK, 135 maybe OK without a cleanout. And of course the trap arm length is limited, so the feasibility depends on the sink being close enough to the column.

Also, at the end by the column, you would have various ways to take off the vent and connect to the stack. What you've drawn looks like an upright combo for the vent takeoff, then a san-tee to join the stack. That could instead use a combo to join the stack if desired for some reason. You could also use a san-tee for the vent takeoff, then your vertical sink drain would join the stack via a 45 and a wye.

Cheers, Wayne
 
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