I wanted to update a comment I left in 2023 that said you could manually purge deleted forms/other things by running the following command (er, running with --help won't purge anything but will give you more flags, like the -f flag, to use):
docker compose exec service node lib/bin/purge-forms.js --help
In 2024, we started allowing more things beyond forms to be purged, and wound up renaming that script. The functioning command is (as of Jan 2026):
docker compose exec service node lib/bin/purge.js --help
I apologize for that outdated and broken command leading people astray!
This purge command will remove blobs, including "cleared" submission attachments, from the database. I imagine that will make running vacuum on the database a lot more effective.