Laundry Tub Backup Issue

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supers4

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EDIT: I should point out for code, I reside in Ontario, Canada(Its in my profile, but figured I should mention it in the post

So I recently replaced an old laundry tub for my mother in her basement. The previous one was from the 80s at least, and the fixture had been dripping for quite awhile(and only had hot, because the cold dripped years ago so my father capped it. Because oh yes, this fixture was sweated onto the supply line). So now she's quite happy she has working cold water again in the tub. I also added in an AAV as I didn't believe the basement fixture was properly vented(there are two roof vents on the house, so the system is vented). The issue that is arising is when the kitchen sink is filled to do dishes then drained, the p-trap in the laundry tub bubbles out. Which I assume means positive pressure in the system being generated. Removing the AAV stops the problem. But clearly that isn't a solution as that would mean an open vent inside the house.

As I said, there are two roof vents on the house, it is a split level house. One half has the two bathrooms and they share a vent, and then the kitchen has a vent. The kitchen is directly above the laundry room, the drain line from the sink comes through the floor then runs under the floor joists until it meets the next wall(it can't come straight down as there is a window there). Previously the only "vent" the laundry room had was I assume a "wet vent" as it used the drain line from the kitchen. Issue is years ago I had to do a repair as my father originally had the point where the kitchen and the horizontal line met as a T, and it cracked open. I replaced it with a wye in what I believed was an attempt to reduce the strain on the joint. Maybe that was a mistake? Did that suddenly remove it's ability to vent?
The new system has an AAV, which I thought would fix that problem. And it mostly has, in that the laundry tub drains quite well. The issue is when the kitchen sink drains from full(when you just run the water, no issues).

I've attached a diagram of the laundry room plumbing, and a very rough(and absolutely nowhere near scale) diagram of the house system. The two bathrooms on the left of the image are almost right on top of each other, and the vent runs basically through a shared wall in that area from what I know of it. There are no drain issues in that part of the house.
So would this issue mean, if there is a clog somewhere, it must be after the wye, but I assume before the junction where the bathroom stacks come into play? Bathroom stacks are 3" ABS, the lines coming from the kitchen and laundry room at 1.5". Or is the issue that the horizontal line where the kitchen and laundry room come together should be 2" until it meets the 3"?

The original idea for the laundry room was to add in a standpipe for the washing machine, but code required it to be a 2" which would have meant replacing about 20feet of pipe. Since my mother was just as happy to have it drain into the laundry tub as it always had, it was decided against changing out all the 1.5" pipe.

So my understanding is, I have positive pressure building up between the wye and the trap under the laundry tub. And so the only way to relieve it, is for the trap to bubble until the system balances itself(or the kitchen sink finishes draining).

Could the roof vent be clogged? Would that cause the problem in the lower floor? or could the drain line be partially clogged to the left of the wye, between the wye and the connection to the 3" line? Or am I missing something entirely?

This was a problem years ago, and the solution then was to install a leftover flow-valve from a sump pump behind the washing machine along the horizontal stack. It, worked, but when adding in the AAV that check valve was removed because it was full of soap gunk, and I presumed to think the AAV would solve most of the issues.

Hoping you guys might have suggestions or solutions to this problem. I do not have access to the kitchen vent stack, as it is buried in a wall, behind the kitchen cabinets. I do not foresee my mother agreeing to let me go on an adventure of ripping up her kitchen. She'll likely just accept that it's been like this for years, so let it be. Unless I can run a line to the right of the laundry tub, up that wall and tie it back into the kitchen drain(but I'm not sure if that would solve the problem, as it's just another wet vent, and might just cause the drain to divert itself at whatever fitting I use there?) Or maybe it is a clog, and I'll have to get my hands on a snake(and find or add in, a cleanout in that area. There is a cleanout on the horizontal line from the kitchen, then there is one at the 3" line. I do not think there is one elsewhere that I am aware of at least, not until the connection to the main sewer line at the far end of the crawlspace. If necessary, I could cut in and add one by the wye if the one in the ceiling doesn't work.

Edit2: So after looking at the plumbing coming down from the kitchen, I have noticed the horizontal run has a sag in it. This will be fixed shortly; but could this be causing the issue? It's a 5' run, but end to end difference is less then 1/2" drop, with the middle sag having about an 1" difference. My solution to fixing it is cut the vertical drop coming from the kitchen and shortening it. I'm not sure if this could cause the problem given it's before the wye. But figured the most pieces of the puzzle offered, the better odds of finding a solution.
 

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John Gayewski

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The sag could be causing this. Your laundry drain and kitchen sink drain should both be 2" with 1.5" traps.
If this is all 1.5" piping that could also be an issue.

I would first fix the sag. Then check the piping/vents for clogs (kitchen sink drains tend to build up crap inside of them making them even smaller), then change 1.5" piping for the drains to 2". Which should help with airflow. If all this fails run a vent to atmosphere. It really depends how far your willing to go with this I guess.
 

Jeff H Young

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Its probebly plugged somewhere, the sag might be trapping the vent . Bad work one thing after another even if house was built that way hard to pinpoint.
How about trying this ? remove p trap at laundry sink run kitchen sink full blast for like 10 minutes, fill kitchen sink full and pull plug if water comes out where p trap was you got a drain blockage plain and simple . of cource I dont want a mess in the basement but take the guess work out and be prepared for a spill.
 

supers4

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Thanks for the advice. I intend to fix the sag this weekend, then try out the idea you suggest Jeff to see if there is a clog. Might pick up an inexpensive drain auger just incase. Unless I can find the old snake my father had, might be stored somewhere in the crawlspace.
I'm also going to sit down and work out the potential costs of replacing it all with 2", if I have a more firm number my mother might be inclined to agree to spend the money if the above doesn't fix the issue. And then when she goes on vacation in the summer I'll likely be the nice son and just do the work anyway if she doesn't agree at my expense lol.
 

JimZaccaria

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Thanks for the advice. I intend to fix the sag this weekend, then try out the idea you suggest Jeff to see if there is a clog. Might pick up an inexpensive drain auger just incase. Unless I can find the old snake my father had, might be stored somewhere in the crawlspace.
I'm also going to sit down and work out the potential costs of replacing it all with 2", if I have a more firm number my mother might be inclined to agree to spend the money if the above doesn't fix the issue. And then when she goes on vacation in the summer I'll likely be the nice son and just do the work anyway if she doesn't agree at my expense lol.
The things we do for our mother's, right? lol
Not sure I'm qualified to offer advice here, as I'm also working out some venting issues on My Mom's old 60's vintage house.

There were some back-up issues at the kitchen sink... I realize there are NO Plumbers in a Bottle, and yet... Zep products seemed to work quite well on clearing the apparent blockage... the last I put down was their Enzyme formula to hopefully eat up some of the old build-up in the drain lines. Though the back-up is cleared, there is still some significant gurgling in kitchen sink when the washer drains, which had led me down a road I'll likely put in a separate post to seek advice on from the Masters here.

Thank God you at least have a crawl-space... Mom's house is on a slab, which "I" will Never get under.
 
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