Using "Repository Manager" you are restricted with only being able to delete the number of content items in one hit restricted by a configuration variable which is by default 200.
So, in case there is a need to cleanup all content items in the repository and you have thousands or more, following is lot less clicks:-
- Create an Archive, for ex, "ToDeleteAllContent"
- Set the Export Query as " dDocName like '%' " and Select the option that indicates all revision
- Click Export and select "Delete Revisions" .
- Once the export is finished (you can close the window and check back status later if there are lots and lots of items), just delete the "ToDeleteAllContent" archive itself.