Can Someone Explain the Waste Pipe. Sink/Dishwasher

[adzyp]

Im just disconnecting my dishwasher ready for a new one and had the dishwasher waste pipe taken off. I then poured some water down the sink and lots of it came out of the connection where the dw waste pipe no longer is.

So i can only assume that when the pipe was connected, waste water i was pouring down the sink was making its way down into the dishwasher. No wonder it didnt smell great at times!

I was just wondering if this was correct? Seems as though this shouldnt be happening but all the pipework seems to be setup that way so can only think that it is right?

Ive added a pic and the red circle is the dishwasher pipe.

Can anyone shed light on this please and if it is correct is there any way to reduce it so im not getting dirty waste water going into the dw

 

[denso13]

It's all piped up correctly. Perhaps take the trap off and check everything is running freely. Sounds like something is backing up.

 

[copea]

The waste water is taking the path of least resistance.
If it's only happening when you're draining a sink full, I wouldn't worry.
If it's doing it when you're draining just a couple of litres, as Denso says, you could be looking at a partial blockage somewhere.

 

[Steelmasons]

The waste hose of dishwasher should rise above the spill level of sink bowl.
Industry gone to the dogs what with all these extension traps etc...had the waste for dishwasher been installed correctly in the first place you wouldn't be having this issue.