Just completed our first trip with our new travel trailer

How do you fill the tank, with a garden hose squirting in a large inlet (gravity fill) attached to the large white hose in the photo, or do you have a valve to direct city water (pressure fill) to the tank?
Usually if you have a gravity fill system the vent hose follows the large fill hose to a screened vent.
From what I can see, water will follow the hose you installed and dump against the belly. That will happen while filling and on the road. What is to keep dirt out of the vent?