I found this link that describes one way to solve your question, but you'll need to download a script from Ubuntu Forums and I couldn't get it because I'm not registered there. I assume that it will work, but I don't know that for sure.
Another solution is to go back to the Unity Desktop instead of the current Gnome Desktop that you're using now. The Trash Can was always included in Unity on the Favorites bar, and it is still there if you choose this method. This link gives good directions on how to return to Unity. (When configuring, note that you'll have to "arrow down" to choose the lightdm display manager, then TAB to highlight the OK selection, then Enter. The mouse doesn't work in these configuration screens.)