I setup each of my Samba shares to delete old files in the .recycle after 30 days. I just checked and I had files piling up since I setup the Samba share.
It looks like the daily anacron job should have been ensuring this was done:
run-parts --regex='samba-recycle-*' /var/lib/openmediavault/cron.d &>/dev/null
But it evidently wasn't working.
I cleared them out myself with this:
find $RECYCLE_DIR -atime +$LASTACCESS_MAXDAYS -type f -delete
find $RECYCLE_DIR -type d ! -path $RECYCLE_DIR -empty -delete