sooner or later you will run into a point in time, where os x will not allow you to empty the trash. sometimes this is due to a locked file, incorrect permissions etc…
well you can use a nifty freeware apple script called trash it or you an open the terminal and use the following command.
sudo rm -rf ~/.Trash/*
make sure that the command above is typed exactly as shown or you may screw your drive up pretty bad [i.e. delete everything on your hard drive]. so use caution when using this command.