For purging entire recyclebin in a multitenant environment as of now you can only query each pdb recyclebins with:
select name,a."b" from (select con_id,count(*) "b" from cdb_recyclebin group by con_id) a natural join v$pdbs;
then jump into each affected PDB with "alter session set container=****"
then "purge dba_recyclebin"
So, it would be nice to have an "purge cdb_recyclebin" which can be run from cdb$root, beside "purge dba_recyclebin"
Peter