I think you have the wrong end of the stick.
When deleting a topic in the forum all the replies are also deleted.
The problem with access is when you delete anything it isn't actually completely deleted, it remains in the database but unavailable and not seen until a compact and repair is run when the deleted items are completely removed from the database.
This doesn't matter what application you are using or even if you have your own access database and delete a record directly in access, until you run the compact and repair your database will slowly grow insize.