by Laurent Wafflard.
Due to an issue of the external backup space (backup_auto_destination), we also had an explosion of space consumed on moodledata.
The script attached (in french, sorry) :
list the automatic backups stored on moodledata
can copy them elsewhere ("demo" = dry-run, nothing is actually done but it show what would be)
can delete them (with "demo")
It should be stored at the root of Moodle files (the same level as config.php). Only a Moodle Administrator can call it (http://moodle_url/purge_autobackup.php)
DATE_BACKUP at beggining of script limit action to a specific date or year.
Hope this help.