You still aren’t sure how rv sewer works.
Gray won’t flush any black except whats residual in the (typically short) shared section of main line. It basically flushes the sewer hose out and that’s it.
Beyond that, tank sensors are not always or even frequently accurate.
It’s highly unlikely that you’ve made the poop pyramid and blocked everything up in just 2 weeks of 1 man pooping, lol.
You can look down the toilet and see if you have an issue as well as measure depth of fluid retained.
It’s a brand new camper so possibility of a construction issue is imo greater than a camper that’s worked the bugs out already.
And of course assuming “normal” use and you haven’t used too much poopy paper and not enough water.
Go see what’s left in your black tank visually and if it appears to be clogged or building up, filler up about 1/3 -1/2 full and go take the camper on a short drive to break everything up.
Dumping chemicals won’t do sht for you. Figuratively or literally. Lol
I guess another pertinent question is do you know you have a 2/3 full tank of water and baby Ruth’s? Idk your tank size but that much sewage from one person in a week sounds like a lot?
Report back when you’ve actually verified what’s left in the tank.