We get intermittent back-ups, sometimes the disposer other times it's the main sink on right. There are 2 sinks, a small one on the left with disposer hooked up and a large one on the right. We also have a dishwasher (on the right). Any suggestions for re-doing waste configuration are greatly appreicated. I've attached pictures of current configuration.

The lower pipe doesn't appear to angle down to the drain pipe sticking up out of the floor ("floor pipe"). Check the lower pipe with a level if you wish, and adjust that pipe to definitely angle down by replacing it, and, possibly the piece it attaches to (the vertical one attached to the floor pipe). You may be able to find a flex pipe like the one from the disposal long enough to replace the piping from the trap to the floor pipe, with no intermittant piping. Cut the floor pipe off 3 inches or so, HOWEVER, measure the entire distance for the flex pipe first, including estimating turns. If you can't find a flex pipe long enough, the main thing is to give the lower horizontal pipe downward slope to the floor pipe. BTW, some dishwasher backup happens in many sinks when the dishwasher dumps its water, but it shouldn't start filling up the left sink before it drains through the piping "system".

I think I would repipe like this.

And I think in either case I would swap that long turn 90 pointing down for a sanitary tee and install a AAV on the top so that my sink would be vented.
Regards, Tom

You definitely have a mess under your sink(drainwise). Tom is correct, you need to add a vent(in your case aav would be easiest best solution) Harold is also correct, it need to be repiped. I see two U portions of a trap connected together that hook into an end outlet pipe. Why? Just use one single p-trap assembly, then add an aav and you should be set. Now, fixing all of this may still not cure your problem(but it is the best place to start). If you get all of this fixed, and it still backs up, then you will need to auger the drain. Please let us know if you need further assistance on this. Good luck. Lee.

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To HKStroud:
It's a pie. When I first hooked this up a couple months ago, this was the only pipe secion I had that would accept the end of the trap.

Thanks for your help/suggestions. Just one more, what is an "aav"?

AAV, air admittance valve. STUDOR® | IPS Corporation (http://www.ipscorp.com/studor)

In the sketch above, would I put the AAV in the horizontal section between the two P-traps?

In the sketch above, would I put the AAV in the horizontal section between the two P-traps?

A AAV will mount in a vertical position above a sanitary tee. (see image) Good luck, Tom

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The "Widget Maker" nailed it again. Your sink is now vented. Good luck, Tom