There's always a learning curve with a new camper, but eventually you'll figure it out. First, you can't depend upon the sensors on your holding tanks. There are hundreds of forum threads here about malfunctioning sensors and how to to fix that problem.
The best thing you can do is drain the second grey tank until it's completely empty. Drain the first tank until it's completely empty. Then close both valves. Run water in the kitchen sink for a couple minutes and open one of the valves and see which one discharges water. Then you'll know.
Then do the same thing with the sink and shower in the bathroom. Then you'll know for sure. Labels on your RV don't necessarily mean anything. You can't trust that.
And by the way! You just learned a very important thing about purchasing an RV that all of us have experienced. And how sad, new buyers just don't want to believe the seasoned, old-timers ... and that is ... Salesmen don't have a clue about anything related to RV's! They will tell you anything to get you to make the deal.
