The “Delete locked items” option automatically deletes locked items from Trash without requiring that you unlock them first.

You can force the Trash to empty even locked files by holding down Option and, from the Special menu, selecting Empty Trash. This will remove items even if they are locked. There is no way to move system files to the trash other than using the sudo command, so there is no security risk.

Basically this will do something like:

sudo rm -r ~/.Trash/*