sink and dishwasher not draining (hi-jack split)

This morning my sink did not drain properly. At the same time my dishwasher (whose outlet pipe is attached to the U-bend of the sink) failed to drain properly - 2 or 3 inches of mucky water in the bottom. I have rodded the outlet pipes from the sink so this is now draining better (still not as quickly as it should) . In the bottom of the dishwasher I found this :-


can anyone tell me what this is (non-return valve?) and where exactly does it fit? I can't see any obvious place it has come from....it's a puzzle...
I will be very grateful for any help ('cos I'm doing dishes by hand now...)

Thanks

Tony

Thanks for the responses. I didn't even know we had one of these things! I do have a partially blocked drain, but also it looks like the non-return valve in the dishwasher (Bosch Classixx) is not working i.e. If I fill the sink with water and then pull plug out, the water from the sink goes into the dishwasher via the dishwasher outlet connected to the U bend under the sink. Any idea how I get at this valve and repair it?

(Sorry about the hi-jack previously)

thanks,

Tony

the fault is your drain.

If the drain is blocked, waste water will find its way into the dishwasher

however, the waste pipe from the dishwasher ought to be be looped up, to the underside of the draining board (so that at its highest point it is higher than the water level in the sink) or else, if it passes through a hole in the sink unit, the sink should be right at the top. This is what prevents sink water flowing down the dishwasher waste pipe, not a valve.

washing machine wastes should do the same.

Thanks JohnD. I suppose it's obvious really, but until I had the blocked sink outlet I didn't think about the dishwasher outlet pipe being looped up. Anyway, pipe looped up, sink unblocked and dishy working!
Many thanks for the help, Tony