I deleted files from external hard drive, they are no longer there, trash is empty but space hasn't increased, what do I do?
Launch the terminal / command line, and replacing 'VolumeName' with the name of your drive type:
sudo rm -R /Volumes/volumeName/.Trashes
Each drive has its own hidden .Trash folder, and each user has a folder in that folder. The above will delete all trash folders on that specific drive.