Force Empty Trash Can on macOS
Empty Trash on Startup Disk: sudo rm -rf ~/.TrashIf you are on the external drive, replace the bracketed part with the path to the volume by dragging volume icon on to Terminal window, and run the code.
Empty Trash on External Drive: sudo rm -rf [Volume Path]/.TrashesBeginning with El Capitan, macOS automatically repairs file permission errors behind the scene; so running repair file permission from Disk Utility is no longer an option. You can still run First Aid, if you insist.
Running the codes will empty the Trash, but remember to reboot your computer afterward at your convenience. While the error itself is unlikely to affect your entire computer, —if, of course, the deleted file was not system critical— privilege related errors tend to keep spawning until you restart a computer, even if Finder says you have a total access to the file.