Discussion:
https://meta.discourse.org/t/permanently-delete-posts-topics/7438
Howto:
https://meta.discourse.org/t/tools-to-permanently-remove-or-delete-spam/5289/7?u=elberet
A few things changed since half a year ago, so you may need to adjust some of the commands; e.g. the Discourse docker manager now lives in /var/discourse by default intead of /var/docker.