Washer backs up into kitchen sink, but sink seems to drain fine.

[bennybmn]

Ever since we moved into our house 3 years ago, the washer has backed up into the sink. I know I know... I should have looked into it sooner, but a baby happened almost exactly a month later so... It stayed consistent, only backing up about a half inch depth of water. Recently, I noticed some water around the washer too, I figured out it was actually running out around the drain hose from the drain in the wall (which has a good 8" extension on it.), so it's backing up both ways. When I use the kitchen sink, it drains pretty well. Sometimes there will be an air bubble just below the strainer that  I need to "burp", especially when the strainer is partially full, but then it drains like gangbusters.  

So I called a drain/septic guy to snake me out a couple weeks ago. He went in thru the washer drain and got nothing. I mean nothing. I'm not sure how deep he went, but I don't think that leg is blocked. I don't know how well it's vented, I haven't crawled around in my attic to see what's connected. 

Doing some mild googling, it looks like newer washers can overpower older, 1.5" drain pipes, so most new homes have 2". My house is circa '76. The washer is about 15' from the kitchen sink. We're on a slab (ranch). I'm trying to figure out how improper venting could be the culprit, given that the sink drains on its own. I don't see it... Is it possible I have a partial clog even tho the sink drains? Or is the washer drain simply too small? If so, I don't see how that would make it go into the sink across the room. Should I snake in from the sink? 

Thank you all in advance for your insight!

[Herb G]

My washer does the same thing.
Only, my washer is in the basement & the sink is one floor up in the kitchen.
We had a guy come out & it was tree roots about 75' out in the sewer line.

I'd climb on the roof & check the stacks to make sure nothing is clogging them first.
If the stacks are clear, I'd have someone clear the drain lines to the sewer with a cutter head snake.
It very well could be further out in the sewer line than you think.

I don't think the drain line is too small.

[bennybmn]

So your sink drained OK on it's own, it was only when then washer was draining?

[Robert Adams]

Does this sink happen to have a waste king garbage disposal? 


      If so there is your problem. They have a horrible rubber shield that keeps an air bubble under it because the slits and holes are poorly designed. Once that air burps out itll drain. 

      We have that issue with our sink. It wont drain at all but if i take that stupid rubber thing out itll drain a swimming pool in 10 seconds. Im just too cheap to replace the disposer and too lazy to buy a new seal and punch a bunch of holes in it for air to flow out when water flows in.

[woodhead]

Check for clogged vent piping.


Al

[EricU]

it's quite possible the drain has inadequate venting.  I ended up adding a new studor valve in my mom's house.

[Snipe Hunter]

Check for clogged vent piping.


Al

Go to the roof and snake out the waste vents.

At least you'll know they are clean.

She what happens. 1-1/2 pipes should work but the won't without clear vents.

[Roly]

I'll bet on a partly clogged drain past the point where the two drains tie together.     The washer can pump a lot of gallons quickly to fill the pipes because of a partial clog where the sink would have to run a long time for the same amount of water.    The clog will probably be in the 3" or 4" pipe leading out to main sewer.  Roly

[Phil Thien]

My washer empties into my basement sink, which drains to the sewer at a rate slower than the washer is capable of emptying itself.

[bennybmn]

Thanks all. I still can't wrap my head around how the venting would cause the problem, but it's a simple solution and free to try.

Any volunteers to climb the ladder?