The passenger side is the hot supply from the engine, the driver side is
return.

If you are using the prestone flush system then yes, the hose with the
coupling is the one to use.  Just remove the coupling and insert the T
fitting there.  I would also suggest cracking the lower radiator hose loose
for draining the radiator, it is much faster than using the petcock.
Remember to use pure antifreeze and not that 50/50 crap when you refill the
radiator after the flush and put it into the radiator unmixed.  It will mix
with the water that is still in the engine to give you the proper ratio.  If
you want to do it with the distilled water method as some in here like to
do, then after the flush you will need to remove the lower radiator hose as
well as the block drains (small hex fittings on the lower block on the sides
of the engine) to remove as much water as possible before filling it with
either that pre-mixed stuff or an equal amount of distilled water and
antifreeze.