The center hole on the pump goes to the engine..
outer hole on the pump is the outlet which
will supply oil to the filter.. the port on the
pump that is plugged isnt used.. that was used
in the machining process and is a cross drilled
hole.. it has a plugged port in there also
EDIT
this is how the SB works.. but the center hole
on any filter is always the return going TO
the engine
EDIT
the outer area of the filer is much larger so it can
filter more oil before getting plugged up