How can I add Trash icon to the sidebar in Mac OS X Lion? How can I add the Trash icon and empty Trash from the sidebar of Finder.app in Mac OS X Lion ? 

I dont have a problem to add them in the list of favorites too, but the Trash icon is not draggable.
First, open the trash can by clicking on it in the Dock.
In the Finder, press Command-shift-G (go to folder) and go to ~/.Trash
In the Finder window for .Trash, click the proxy icon in the title bar of the window and drag it to the sidebar.
You then have a trash folder in your sidebar.

To empty the trash from the sidebar, open Automator and create an application.
As the sole action in the application, select "Run AppleScript" and use this AppleScript:

on run {}
  tell application "Finder"
    empty the trash
  end tell
end run


Save the application as "Empty Trash", and drag it to the sidebar.