I use the winterize suction hose on the pump then connect the outside shower hose (adapt as necessary) to the water fill connection. Turn on pump. Removes water from jug, pumps it to outside shower and into the tank. Simple enough.
I was lucky in that my "outside shower" is actually a standard male hose bib connection with a garden nozzle. If yours is something else you'll have to go to Lowes and make up some kind of adapter to get from the shower fitting to the water fill female hose bib connection.
Only extra part is the adapter. Everything else came form the factory.