Default data directory

Hello,

We're building a test box for our webmaster to play in.  It needs to
have the same config as his production box.  The postgres default
data directory doesn't match the location of the data directory
location on the production box.  The postgresql.conf file has the
line that says that it changes the default data location commented
out.  Is there somewhere else that postgres can get this information?

I can't figure out how the Postgres that's running on the production
web server knows where to look for its data.

Thanks,
Carol