[Penguinfan87]

I live in a 2 story house.. it has 2 kitchens both drain using same line.. when we let the water out in the sink in the upper kitchen it backs up in the kitchen sinks below.. I've tried drano.. didnt work.. I plunged until I can't plunge no more but when I do that I see black stuff come up and the water level will drop a little.. I also tried using a snake but this is an old house and drains twist and turn.. please help me find another solution.. thank you

[Stratmando]

The clog is below both, and after they join, If a snake doesn't work, or through roof vent,
I would try plugging off downstairs sink, and dump a drywall bucket full of water through roof vent, fast. Possible it could back up through shower drain, or toilet. I personally have had excellent Results and no problem, just lucky. A qualified or experienced plumber may provide better answer. My trade is Electrical/Electronics.
-------------------------------------
Had problems with bath sink, went to roof and duct taped shopvac extensions to vacuum through roof vent, and it sucked up a lot of rust scales. Solved problem. It happened after new roof was installed in older house, Cast Iron pipe, When they hammered the lead around the vent, it broke free the scales, clogging at the Elbow.

[biggsie]

I agree with Stratmando, the drain is plugged below bottom sink. I also had thought of

Using a powerful wet and dry vac or 2 vacs for more power to pull blockage back out

The way it went in... The main thing is to seal off the vent and the other sink drain on

This run, I would remove trap on lower sink and try to suck out the problem from drain...

Hope I have explained things clearly enough...