How do I hook up the drain when installing a one- piece fiberglass bathtub drain

[lpk8]

I have no access from outside the room behind the shower controls and with the walls already a part of the unit how is it done ?

[Cass]

I am going to suggest you call a plumber or plumbing company that knows how to do this, has been in business a long time, and will guarantee the work against leaks, and have them do the work.