The non-pressure, as Roy mentioned, is for filling your fresh water tank. It is basically a funnel down to the tank with a small vent line (black screened opening).
The one with the female connection (black plug) is where you would hook up the city water supply. Pull out the plug to attach a supply hose; make sure there's a strainer with a gasket installed.
The one with the male threads (white MAS cap) is your sink drain.
Pop-ups, unlike many larger trailers, will not fill the water tank from the pressurized city water supply connection.
