i really couldn't tell. thought the two close together were for city hookup and fresh water holding. i can see where they might have to mount the black water tank flush in close proximity.
u probably can't see up underneath but my black flush has a vertical loop with a vacuum breaker on it.
the city connection and the black flush are the only two that i can connect a hose to. on mine, the fresh water tank fill also has a vent above it.
was trying to figure another way to identify them other than hooking up and seeing what happened. can see if u hooked up to the black water flush, u may think u r filling the fresh water tank. guess if u hook up and water stops flowing, ur on the city. if all the connections look alike, it would be trial and error to identify the other two.