Dishwasher water backs -up in sink.

I have a problem with dishwasher water backing-up into the right sink while the left sink is stoppered and in use. If left sink not in use all drains well. Possible plugged air vent somewhere? Awhile back I found the tub drain very plugged with hair etc., removed that and problem disappeared temporarliy. Re-checked tub today and was still clean. Could use help with diagnosing the problem.
Sorry, first post and no time to research all previous posts today. Thanks for any help and patience for a new guy.

 

How is the dish washer hooked up under the sink? Can you take a pic and show us? That will help..

 

Sorry I missed your reply and thanks for replying.

I can take a picture later today but can explain the set-up anyway.

The washer water discharge hose exits the bottom of the washer , extends up and over in a large loop
(attached to the cabinet back with the loop higher than the sink drain) and attaches to the garbage disposal directly above the cross pipe that attaches to the left sink drain above the trap.

Hope this will help,and thanks for any advice.

Mark

 

Ok so a disposal...

Has it always done this?

The sink that backs up is the opposite of the disposal correct?

There are many ways your plumbing could have been done.. Some right, some wrong.. Center waste, side waste... two traps, and different tee placements to connect both sinks..

 

You probably need your drains cleaned.
However, if your disposal has a straight pipe coming out of it, this will add to the problem. Disposal should have an elbow attached, connected to a baffle tee that helps direct the water downwards.
You may not be able to change your configuration as it should be if your trap is too high, you won't have room for the baffle tee. See Picture of correct install.

If your disposal doesn't have that elbow, than trap must be too high. You would have to go into wall and lower sanitary tee and trap.

 

This never used to happen. The sink that backs up is the right side sink with the disposal(the side the dishwasher drains to) and only when the left hand sink is stoppered and in use, otherwise it drains fine. It's like if the left side sink drain isn't open to ambient air pressure it really slows the water flow down and only then does water back-up into the right side sink(but still barely enough to cover the bottom the sink. Pipes/trap/disposal to the wall are all clean. Worked fine for a week or so about a month ago after cleaning out the tub drain pipe but problem is back. Very small house and I do believe all pipes lead to same vent pipe and are all clustered within a couple of feet.

I will take a picture and post later today or tomorrow.

Thanks for your guys help. I know this isn't an earth shaking problem, but one that just bugs me because it never used to do it and I hate it when I can't figure things out.

Thanks again

Mark

 

There is no reason I can think of that the disposal side will run slow when the other side of sink is plugged and in use..

Turn on the disposal when this happens. Does it drain fine? ( Is this a new disposal?)

 

Yes Mike and Bit,
The baffle tee I mentioned aids in preventing the opposite side of the sink (from the disposer), getting flooded. If the disposer side is flooding, sounds like a vent problem.

 

This is the photo

This disposal is connected just like the old one and the dishwasher is original 1984 so don't imagine it has a high power water pump. Like Handyone mentioned about a vent problem, could the vent through the roof have become partially plugged with leaves, nests, anything?

Let me know what you think about going about checking that kind of stuff.

Thanks very much.

Mark

 

It would be worth a shot to have someone come out and clean out your vent pipe from roof.

If you have cast iron pipes, it would also be worth it to (down the road) have your sanitary tee replaced.

The wall would have to be opened up, cast iron cut out, and replaced with ABS.
The ABS flows much better than the old cast iron and your slow drains will be a thing of the past.

 

The vent has nothing to do with it... Its something else. ( Vents are for other fixtures not to suck the trap dry. They are not for flow of water down the drain)

So you fill the left sink with water with the stopper in right?

Then you drain the DW and the right sink backs up some?

And if the left sink is empty and stopper out the right sink drains fine with the DW draining?

Try the scenario with the left sink plugged and filled and run water from the tap in the right sink... What happens?

 

I have read that cleaning the vent pipe from the roof(one said to try and flush it with water to clear possible obstructions) has worked in some instances. All my pipes are ABS. May try that.

 

Correct, right side sink backs-up when DW pumps out water only when the left sink is stoppered.
If left sink is not stoppered, no back-up occurs and drains normally.

Also had a guy that used to do plumbing tell me that even though it sounds crazy, if the DW discharge hose is partially plugged and slows the water flow that it could cause this problem. Says he has seen it happen numerous times. Another thing to try I guess.

I appreciate everyones help and will figure it out somehow.