Trash is full when external hard disk is plugged in

Whenever I plug in my external hard disk, I notice that the trash becomes full of the files I deleted from my external hard disk. It seems to be quite a massive amount of files stored in there, and I was wondering what would happen if I were to "empty trash" while my hard disk was plugged in. Would it remove the deleted files or would I risk having also the other files (which I do not wish to delete) on the hard disk emptied? I'm scared I'll loose my hard disk files; help!