[Answer ID: 14207]
The trashbox directory is your recycling bin. When you delete a file off the TeraStation is gets moved to the trashbox.
If you want to empty the Recycle Bin (ie the trashbox folder), all you need to do is delete the trashbin folder.
If you would like to get ride of the trashbox, disable the Recycle Bin option for the Share Folder.
You can do this by logging into the TeraStation's settings, navigate to Shared Folders - Shared Folder Name, and disable Recycle Bin.