In Mac OS X, when you try to empty trash, a warning message would be displayed “Are you sure you want to permanently erase the items in the Trash?“
If you do not want this warning message to be displayed then you can turn off the message using the Finder Preferences.
Click the Finder and select Preferences from the menu list.
In the Preferences window, navigate to Advanced tab.
To turn off the warning message, un tick the check box with label as “Show warning before emptying the Trash“.