The best way to add the Trash icon in your Ubuntu Desktop is the following:
To create a new file ~/Desktop/Trash.desktop.
The contents of the file are:
[Desktop Entry]
Comment=Contains removed files
EmptyIcon=trashcan_empty
Encoding=UTF-8
Icon=trashcan_full
Name=Trash
Name[en_US]=Trash
Type=Link
URL=trash:/
