Hi,
You can add a cronjob that will delete files older than a week. If the files are located at some place other, locate its location and change it accordingly in the cron job.
#Deletes fax files older than a week
0 3 * * * /usr/bin/find /var/spool/asterisk/fax/ -type f -mtime +7 -exec rm {} \; > /dev/null 2>&1
Thank you,
Daniel Friedman
Trixton LTD.