Can the recyclebin be turned off for a container database but remain on in a pluggable database?

Yes, the multitenant architecture allows this.

SQL>select name, value , ISPDB_MODIFIABLE from V$parameter where name = 'recyclebin';

NAME                           VALUE                ISPDB
------------------------------ -------------------- -----
recyclebin                     OFF                  TRUE

Switch container to a PDB:

SQL>alter session set container=veg7;

Session altered.

SQL>show con_name

CON_NAME
------------------------------
VEG7

SQL>select name, value , ISPDB_MODIFIABLE from V$parameter where name = 'recyclebin';

NAME                           VALUE                ISPDB
------------------------------ -------------------- -----
recyclebin                     ON                   TRUE

Remember that the pluggable database must be closed and reopened if you toggle the recyclebin on/off:

SQL>alter session set container=veg7;

Session altered.

SQL>alter system set recyclebin=on container=current scope=spfile;

System altered.

SQL>alter pluggable database close;

Pluggable database altered.

cdb>SQL>alter pluggable database open;

Pluggable database altered.

If you want to toggle the recyclebin on/off for the container database, the procedure is the same except that the entire instance will have to be bounced.

How to purge objects from the recycle bin

sqlplus / as sysdba
purge dba_recyclebin; --> purges all recyclebin objects, globally
purge tablespace user_data user scott; --> purge only scott's Objects from the user_data tablespace
purge tablespace user_data; --> purge all recyclebin Objects from the user_data tablespace

conn scott/tiger
purge recyclebin; --> purges scott's recycle bin only

The next statement purges the specified object from the recycle bin. The first example refers directly to the system-generated name of the object, the second is refering to the original name of the object.

purge table "BIN$W/n28BqBgRbgU64JAQoz3A==$0";
purge table emp;