I often forget to empty my Trash bin. Perhaps because it is located in the least interactive area of the desktop. This includes both the dull Unity launcher Trash icon and the classic menu grey Trash Bin at the bottom right corner. A better alternative can be to empty trash from the App indicator menu (system tray), as it is a more interactive part of the desktop which contains App indicators for Skype, Evolution mail client, Gwibber and the like.
You can empty and view the number of files in the Trash from right-click menu and open the Trash window by left-clicking on the system tray icon.
You can get the Deb package of Trash Indicator from the download link given below. Just double click on the package after downloading it to install Trash Indicator via the Ubuntu Software Center.