Todd from Calgary wanted to convert his portable dishwasher into a built in one but couldn't find the parts. In fact most of the manufacturers do make special kits to accomplish just this, so contact your manufacturer.
Basically you need to put a Y joint in the drain just below the sink and before the trap. That way when the water flows out of the dishwasher with force from the pump, it will not tend to back up into the sink, but will be directed down the drain.
For your information Tod had an Inglis dishwasher. Conversion kit: p#20102991 Price - $75