[Dovecot] Need a quick, safe method to empty /home/user/Maildir/{.Junk, .Trash}

[Jeff Kowalczyk]

I have some (Thunderbird client, dovecot-1.0.13, Maildir) users who get an
appalling amount of spam-with-attachment, and it's causing backups to take
an inordinate amount of time.

I'll implement some quota and server-side spam management when I go to
dovecot-1.1, but in the meantime:

What is the safest way to empty all messages within, but not delete, the
following folders from the server command line:

/home/user/Maildir/.Junk
/home/user/Maildir/.Trash

I don't want the Thunderbird-2.0.14 client to report corrupt
indexing, or worse not show the folder at next use.

Thanks.