You can reformat it? That's apparently the quickest way. Or else it will take all night, but it will eventually delete everything. It took me under a day to delete around 593GB. Probably 15 hours.
Either enter time machine or initiate a time machine backup so that it mounts the drive. Once the drive is mounted it should show on your desktop. After that, it will show in Disk Utility.
Either enter time machine or initiate a time machine backup so that it mounts the drive. Once the drive is mounted it should show on your desktop. After that, it will show in Disk Utility.