kitcken sink backing up

[Sockmonkey]

I have a kitchen sink upstairs and downstairs. When the sink upstairs drains, it backs up into the downstairs sink. Is there any cheap way to fix this?

Someone mentioned to me you can get a one way valve for the sink drain.

Any ideas? Thx

[mark Ransley]

You have a clog somewhere below the kitchen, the lower sink. Start with draino.