Any way to delete forum topics permanently?

Hi all,
I've noticed when i delete a topic on BP and then recreate it, it gives the new topic a number. This must mean the original topic name is still there in the database i presume? Anyway to get in there and clean this out?

Also, when you delete a group does it really delete it or is this the same there too?
If they are in the DB, can this affect performance?