From my wife yelling about the shower water building up in the shower pan, and me pulling the gray#1 lever that fixed the situation, I have deduced that grey #1 is the shower, and gray #2 is the kitchen on my Bighorn. Your results may vary.
An early purchase at WallyWorld after getting the Bighorn was a labelmaker. Now the dump handles are marked as "Shower" and "Kitchen" as well as the tank monitor readouts (for whatever THAT is worth!).
Most people like to keep all 3 valves CLOSED while hooked up in a park, so that when you DO dump the Black tank, you can then flush out the pipes and the connector hose with large volumes of the cleaner, soapy, kitchen and shower waste water.