Click with the right mouse somewhere on the Desktop, and from menu choose Create New > Link To Location (URL).
By default, there is no Trash can on the KDE4 Desktop. But you can simply add it.
Click with the right mouse somewhere on the Desktop, and from menu choose Create New > Link To Location (URL).
Enter Trash or what ever you like as the File name, in the Enter link to location (URL): enter trash:/, and click on OK.
...and here is brand new Trash can on the Desktop.
