I was always wondering how to stop the recycle bin’s pop up every time I tried emptying it, and finally found it accidentally this evening.
If you go “Finder / Preferences” (Apple key + comma) and click the advanced tab, you can uncheck the “show warning before emptying the Trash” option et voila! - job done!
I also noticed an “empty Trash securely” option. Why Apple insist on capitalising Trash I do not know - guess they see it as an application name!
Doing some googling, and with regards secure deleting Apple state:
Even after you empty the Trash, deleted files may still be recovered by using special data-recovery software. To delete files so that they cannot be recovered, choose Finder > Secure Empty Trash. Files deleted in this way are completely overwritten by meaningless data.
Worth turning this on for the paranoid. Although if someone is rooting though your file system, you may have bigger problems!