Upstairs uses washing machine, our kitchen sink backs up.
September 12, 2022 6:18 AM   Subscribe

I live in a two-family house, one on top of the other, and we've been getting periodic kitchen sink back-ups. It seems to happen when the upstairs unit uses their washing machine. What is happening and how do we fix it?

I've snaked my kitchen drain and the drain stack with a 25-foot drain snake and that haven't encountered any blockages. No other drains in the house in either unit are backing up.

The washing machine in the upstairs unit is located near their kitchen and seems to drain into the kitchens' piping.

We live in a 100-year-old house and things were cobbled together in weird ways.

What is causing this issue? How can we fix it? Who do we call?
posted by msbrauer to Home & Garden (12 answers total)
 
I think this is a problem outside the scope of most civilians. But a plumber should be able to help you!
posted by corey flood at 6:29 AM on September 12, 2022 [2 favorites]


(I don’t have any answers other than this used to happen in my -1920’s childhood home with the 1st floor washer and the basement bathroom sink)
posted by raccoon409 at 6:29 AM on September 12, 2022


What is causing this issue?
There is a partial blockage in the drain somewhere after the two drain lines merge. Because the washer puts out a high volume of water all at once (faster than it can flow past the blockage), the water backs up to the common point of the drains, at which point the water will flow until the height in the two columns of water (drain pipes) are equal. Because the sink is lower than the inlet for the washer, the first place the backup can escape is the sink.

How can we fix it? Who do we call?
Clear the blockage. Depending on the plumbing, it may be further than your 25' snake can reach, or it may be that you punched through the blockage but did not completely remove it. Any plumber/drain cleaning company should be able to handle this issue.
posted by yuwtze at 6:49 AM on September 12, 2022 [5 favorites]


It might not be blockage; it might be that the drain pipe shared by the sink and the washer is too small (i.e. it was not originally sized to accommodate the outflow of a washing machine - especially likely if your house was not originally constructed with upstairs laundry).
posted by mskyle at 7:56 AM on September 12, 2022 [5 favorites]


It might not be blockage; it might be that the drain pipe shared by the sink and the washer is too small

I think it's a blockage - a 1/2 pipe can handle about 15 GPM at normal flow - a wash machine is a powered flow so it's probably a bit more. So an old school washing machine using 20-40 gallons would at worst cause a back up for 2-3 minutes. Does that sound right or does it last longer?

Most indoor drain pipes are larger than 1/2 inch, so they could clear it in less than 1 minute.
posted by The_Vegetables at 8:15 AM on September 12, 2022


Response by poster: So an old school washing machine using 20-40 gallons would at worst cause a back up for 2-3 minutes. Does that sound right or does it last longer?

Today was about two or three minutes. I think it's a newer washing machine and front-loading, so should be more efficient with water. Last week we had a backup that lasted for about 20 minutes and may have coincided with when the upstairs dishwasher was running. It was quite a bit more water.

We frequently get a little backup (a little bit of water and then disappears after about 30 seconds) when we run our own dishwasher as well.
posted by msbrauer at 8:24 AM on September 12, 2022


Are you septic or city sewer system? We were having periodic gurgling in the kitchen sink from the upstairs shower and it turned out we had to dig up our entire yard and replace the ancient cesspool system in the yard. The shower was just the symptom of the larger problem. if you have something lower, like a toilet on the ground floor, that is not backing up, then that is a good sign that it's NOT the septic (if you have one).
posted by archimago at 9:18 AM on September 12, 2022


Response by poster: City sewer system.
posted by msbrauer at 9:26 AM on September 12, 2022


I am not a plumber but from a physics standpoint I think (???) improper venting could also be involved, perhaps (???) more so in a 100 year old house. Just a thought.
posted by forthright at 9:54 AM on September 12, 2022 [1 favorite]


We had a similar problem when we lived in a basement unit in a 100 some year old place in Chicago. The cause for us was at the point where our pipes connected back to the city sewer. My memory is fuzzy, but the pipes were slightly misaligned (I think they were connected by a sleeve of some kind?) and we'd get build up that they had to use a hydro jet to clear out. It was something that had to be done every year so, I think.

It specifically had to be the jet cleaner, snaking wouldn't work. The year we lived there they kept sending out the non-jet guys and it was a whole thing. I'm not sure if the same thing is happening with you, but I guess sometimes snaking doesn't cut it.
posted by ghost phoneme at 10:37 AM on September 12, 2022


25 ft. isn’t that far.

Given that this is a kitchen line, multiple kitchens since their dishwasher is implicated, and that no other sinks are backing up, I think this might be a fat buildup.

I would try a heavy dose of enzymatic cleaner overnight, followed a day later by lots of very hot water. Taking suitable precautions so that there’s no risk of anyone getting scalded, you could turn up the temp on your water heater for a day and run a tankful down that drain.
posted by jamjam at 10:56 AM on September 12, 2022


The issue could be...
A) A blockage in the drain line downstream of your sink.
B) The flow from the washing machine simply overwhelming possibly undersized (by today’s codes) drain lines.
C) The 100+ year-old cast iron drain line has finally collapsed somewhere down the line.

You’ll need a real plumber to figure this out.
posted by Thorzdad at 4:28 PM on September 12, 2022 [2 favorites]


« Older Friend died by suicide, I haven't coped with last...   |   What's nicer than a Kallax? Newer »
This thread is closed to new comments.