Deleting attachments stored in ExternalStorage

We’ve been using ExternalStorage to disk successfully for a little while, and we’ve now got 26GB stored.

I note in the documentation that it’s not compatible with rt-shredder, which we’e been using to clean up the database and deal with GDPR retention concerns.

Is there a way to safely delete items from the external storage system? Eventually there’s a chance it will fill the disk it is pointing to.