Window Monkey keeps track of the patterns assigned to each folder by placing a small, invisible file in the folder. If you were to do this with the trash folder, the file would be deleted every time you emptied the trash, and the pattern would disappear.

Because of this, the current version of Window Monkey doesn't allow you to place a pattern in the trash can.

A future version of Window Monkey may allow you to put a pattern in the trash can by handling it in a special fashion that doesn't require a file.