I found this at OTN:
1) Eventually, they will be removed automatically, so you don’t need to do anything to remove them.
2) If you want to purge everything in the recycle bin,
PURGE recyclebin
PURGE dba_recyclebin
3) If you want a particular object not to go into the recycle bin
DROP TABLE <<table name>> PURGE
Justin
Distributed Database Consulting, Inc.
http://www.ddbcinc.com/askDDBC