Hello,
I assume you have Enterprise Vault 10. As far as I know, EV11 is not available (yet).
There is an extensive technote on SQL maintenance for EV databases. Check this: http://www.symantec.com/docs/TECH74666
In addition, you do NOT purge data from EV databases. The only TABLE I know can be purged (to be recreated by provisioning) is the ExchangeMailboxEntry table in the Directory database. The remaining databases will be maintained using the above mentioned document. If you configure Enterprise Vault to do (for instance) storage expiry on archived items, EV will take care of removing entries from the databases affected. When that is done during normal business, your maintenance plan will take care of managing the databases.
You can do some housekeeping on the monitoring database (http://www.symantec.com/docs/TECH72170) and the audit database (if auditing is enabled) (document to be found.... )
If this does not answer your question, can you be more specific in what you see, want, and expect?