I think you might be asking how to get a list of volumes that will be
deleted by the command.  Is that right?  You might try

select volume_name from volhistory where backup_operaton is not null and
location='THE STRING YOU USE TO DENOTE OFFSITE' and
date_time<(current_timestamp-(1 month)-(7 days))

to get your list of dbbackup volumes to return and then run your delete.
You will have your vault return the volumes using the list generated by the
select statement.  I don't know if this will work for you, but it seems to
give me the correct list of dbbackup volumes on my box.  By the way, the -(1
month) part is due to the fact that I'm running 3.1.2.50 and have to account
for the SQL current_timestamp bug.  If you're running a different version,
you probably won't have that problem.

Alex Paschal
Storage Administrator
Freightliner, LLC
(503) 745-6850 phone/vmail