How do I empty a galley tank.

Does this camper have a small outside threaded pipe on the side below the sink with a cap on it? If so it would be the "galley" drain. The small drain from sink to shower and sink, if you have a bathroom, to the drain gate valve would normally be all to the grey water tank and that is what you're seeing in the gauge. Those things can be a pain about sticking at odds levels especially if previous owner want meticulous with NOT running any debris and especially greasy dish water down the drain. Don't care about Park rules, I always wash dishes in a pan and throw it in the driveway if gravel or some other out of the way spot. They don't have to clean my holding tank. You'll know if they're connected if you run water down kitchen sink and tank gets full. Awkward test, sew if it backs up into shower floor. Two person job, running water, checking bathroom and wiggly pulling the drain valve! LOL good luck. We discovered or new old camper DIDN'T have a grey water tank that way by accident when testing everything. Had Crack in shower pan and noticed water on camper floor from there. Fixed that! Now black water tank needs fixed. Vintage campers, God love em. Good luck!