(Posted on one of the Facebook groups the other day, but might be more useful here, as this gets searched/referenced more when people have specific issues...)
In case anyone is having a problem with the gray water valve on a 2021 or 2022 t@b 320... Ours didn't work on our first trip out.. always open regardless of handle position. Figured the issue had to be pretty simple, it's just a gate valve, right? Didn't want to run it to the dealer for something without looking.
I got the belly cover off, and there is a bracket (circled in red below) that holds the cable controlling the gray water valve. In our case it was not held up against the pipe, it was hanging freely. Moving the gray water handle just moved the plastic bracket back and forth.
There is a collar-like piece (circled in yellow below) that is supposed to hold the bracket up against the valve and pipe. Ours was installed incorrectly. I snapped everything together as it should be and it all works as intended.
FYI if you have this issue... Hardest part is getting the cover off!