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

[Bucko]

I had a tough time figuring out a similar problem at my father in laws, pipes were clear, vent free of obstruction and such. I finally by accident was standing back in the basement and noticed an area of pipe about 20' from the kitchen was elevated and not running downhill. I fixed that to run downhill and backflow problem went away. In this case it was backing up into the dishwasher next to the kitchen double sink, good luck with your fix.

[bennybmn]

It backs up with just water too...

[Snipe Hunter]

I had a tough time figuring out a similar problem at my father in laws, pipes were clear, vent free of obstruction and such. I finally by accident was standing back in the basement and noticed an area of pipe about 20' from the kitchen was elevated and not running downhill. I fixed that to run downhill and backflow problem went away. In this case it was backing up into the dishwasher next to the kitchen double sink, good luck with your fix.

 
That will render the waste vent pretty much useless

[Bob10]

Just dealt with an issue like this.  Upper unit woman dumps all kinds of crap in the drain for years resulting in plugged drains that I snake clear vent runs off at a 45 to a larger stack all of it takes place below the level of the sink.  I just discovered that because it was below the sink it allowed for a clogged drain to block water to the point the 45 angle pipe could drain into the vent.  So when the vent rusted out it was readily apparent the drain was blocked I snaked the drain it ran fine but the line of the lower unit blocked up.  By chance I decided to replace the stack above the 45 connection at the vent.  My friend made the cut and asks why the vent is full of water.  Seems the vent ended up being blocked too.  Resulted in replacing that too as the snake wouldn't get beyond the clog.  

Check your vents and then check them again

[mike4244]

Usually the trap is 18" deep if I recall the instructions. Plumbing inspector told me that 24" or more would be better even though 18" was up to code. Took only 15 minutes to replace the PVC drain lines to a depth of probably 30".
This was about 20 years ago for a new addition for my son. I recall he said newer machines pump harder and the extra depth prevents backing up of drain water.
mike

[bennybmn]

UPDATE:
So a while back I went on home adviser looking for a plumber. First guy who called me I had come by, turns out he's really a sewer/drain/cesspool guy, not a full on plumber who could fix venting etc, but I did say I think I need a snake in my post... He snaked down the washer drain and got nothing, but he also didn't charge me! Nice guy.

A few weeks go by, vacation, etc, and we get the name of a plumber from a contractor friend. He sounds like he can't be bothered on the phone, but he comes by a few days ago when my wife (teacher, off for the summer) is home. He says you need a snake... She says I think we did that, but OK. Got the name of the snake guy from plumber guy.

Snake guy comes and says it's probably a partial clog or a venting problem (No kidding?) and suggests we try stuff called "cessflow" before we spend money on a snaking out to the street. Soap/grease/etc can build up, and a snake can go right thru a pile of grease and not fully clean it out. It's $25 a gallon, pour one down the kitchen sink, one down the washer drain, let it work overnight. At this point I'm annoyed that nobody seems to care enough to help us out, but at least nobody charged us. 

So the other day I go to the Depot by my office, they have ONE gallon, and I had to walk a half marathon to find it. So after my son's bed time I go to the Depot by my house and they have like a dozen bottles... It's a white, fairly nondescript, jug inside a clear plastic bag FYI. Says that is completely safe for the environment, biodegradable etc. No idea what it actually is, I assume enzymes etc. Also happens to be made locally. So Tuesday night we pour. Use water sparingly before bed, etc.

It wasn't the suggested full 12 hours before I had to get ready for work, but I rolled the dice and showered
You're welcome, America. My wife sent me a message around 10AM yesterday that she did laundry and NO GURGLING!!! No water coming out of the washer drain pipe either!! So it worked. My plumbing definitely IS undersized... only 1.5", but at least it seems to be vented properly. So $50 for pro drain cleaner is a lot cheaper than $200+ for a full snaking. Lesson learned.

Side note, I think I convinced my wife that hamburger grease should be allowed to cool and thrown in the trash

[Roly]

Remember the guys that did not charge.    You may want to do business with them in the future.   Roly

[bennybmn]

Absolutely have!

[EricU]

after we clogged the kitchen drain, I am now in charge of hamburger grease disposal.  I guess that's better than paying the plumber to come out and unclog it.

[crokett™]

after we clogged the kitchen drain, I am now in charge of hamburger grease disposal.  I guess that's better than paying the plumber to come out and unclog it.

I do the kitchen clean up after dinner. One reason I do that is to limit what goes down the drain. I've cleaned out enough drains in my lifetime.