I just one says Potable water.. Then I'd guess that one is your city water inlet and may ALSO be the fresh supply tank fill inlet (Via a quick fill valve)
The other is the black tank flusher.
Some folks use Y connectors to hook both up at the same time.. And of course when a bit o seepage gets past the safety featurs built in to the black tank sprayer...... Get sick on their own sewage.
Suggestion from Fred (Google RV 101 by Fred) is to disconnect the hose from "The Flusher" when not in use to prevent that.
On mine I have a dedicated rinse hose. IT ends with a vacuum breaker and a check valve and a quick disconnect.. This goes to a short (like six inches) hose to the inlet or the flusher, and rom there to a Vacuum breaker Damon installed, from there to the Tornado I replaced "The Flusher" with, the Tornado has a spring check valve as well.
So i lush with two belts and two pair o suspenders as it were.
And when I'm done, I quick DISconnect (this by the way allows a lot of back flow out the motor home end of the quick disconnect, draining the line up to the vacuum breaker Damon installed)
I've seen folks .. Do it diferently.
Home is where I park it!