Before I start operating on the DB manually, are there any easy options in the AdminCP for removing all Guest topics and posts?

9 hours ago, The Britain said:

Before I start operating on the DB manually, are there any easy options in the AdminCP for removing all Guest topics and posts?

There is an option called Delete Guest Content, but that will delete it for individual guests. It can be found at the Spam Prevention section of the Admin Panel.

To remove the contents for all guests, you will have to run a few sql queries. However, make sure to make a thorough backup of of your database before you proceed.