In KDE4 it is widely accepted that your trashcan shows up only as a Widget that must be added, but I figured out how to get your trashcan into your folder view.
Go to the folder you want to display (Desktop) for instance
Right click, Create New, Link To Location
File Name "Trash" Or what ever
Enter link to location (URL): enter "trash:/"
Click on "OK"
I used my Home folder as an example but Desktop would have worked just as well.
Your trashcan will now show up like this >
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