Automatically purge dropped tables in Oracle
Is there any option to tell Oracle to immediately purge dropped tables?


That would be disabling the recycle bin, if only for the current session. Include ALTER SESSION SET recyclebin = OFF in your build process, or, if this is a development system, you can consider turning it off via the instance initialization parameter. 

Alternatively, you can choose running the build as a dedicated Oracle user; you will then DROP USER ... CASCADE at the end, which will drop all user's tables and other objects without placing them in the recycle bin.