I'd like to clear the blacklist. I uploaded a tarball with three black list entries with the teleporter and selected blacklist (exact) and checked the box for clear existing data. It successfully uploaded.
When I go back to the blacklist, I still have all of the previous entries.
All the adlists and domain lists are kept in a single database at /etc/pihole/gravity.db. You can manipulate entries in that database from the command line as described in this section of the documentation.