I am constantly rewriting the same code for multiple interfaces. How can I work more efficiently?

More interface engines allow you to write code and save it.  This allows for you to do an external code within the interface engine.  For example, Filter by Patient Location is a procedure that you would use multiple times across many interfaces.  Write the procedure (or code) to pass in multiple locations and then pass back a pass/fail flag to the interface.  The pass/fail flag would either suppress or continue to process the record.
I would also recommend that you have a naming convention in place so it is easily recognized by multiple people.