Ok my guess from your description can't see your photos
Your water is coming out the gravity feed .. It's not a sealed system your overfilling the water tank . Once filled ( if that is your intention) your supposed to switch the water over to pressurize the house lines ( should be a valve to do this near where you screw the water hose to the coach ) and stop filling the storage tank.. It's not part of the pressurized system! ;-)water when overfilled is by design supposed to run out to relieve any pressure to prevent the tank from splitting.