Is it possible to just delete all comments?

There are lots of good ones.  But I inherited this derelict board and there is like 30K spam posts.  These are comments on articles.

Perhaps I can create a support ticket that just says... kill all?  

A lot of them are Guest posts, so I don't think they can be pruned with the spam tools the same way you would a registered user.

Any thoughts?

Any retroactive spam tools?

JM