Deleting backups before running a new backup

Hi All

I'd like to backup to a small external hard drive and only store one full image backup. I have other backups running, so I'm not concerned about clearing the drive before backing up

The external HD is 1TB. My backup image is a little over 500GB.

I've tried running a batch file (Pre command) before I backup to this drive which deletes all the files on the target drive.

When I run a backup - it fails with a "Failed to Open Stream' error. I assume this is because it checks what version is on BEFORE the Pre command is run and then it's not there when the backup finishes.

How can I achieve what I want to do...clear the target drive and perform a new FULL backup every time (given that I can't fit 2 full version on the drive)?

Thanks.