If you have to use a threaded connection hose and do not have a gravity fill bib to fill, there will be a valve usually in the closest compartment to where your hose connection is.
This will direct water either to the internal piping system or to the water tank. While filling the tank follow the usual procedure and listen to the escaping air to hear the tank almost full and the escaping air changes tone, and shut it off when it overfills or just before.
As you begin to fill the water tank, also find the water tank drain valve... some people leave them open when not carrying water.