Timely thread.
As it happens I opened up the coroplast under the tanks & valve a few weeks earlier to have a look at how it's all setup should I ever have an issue. Well, the issue came much sooner than I anticipated, and after the last trip I now have a valve that's stuck open. This is on my 2022 2108FBS (bought new in January of this year, only used for ~4 trips).
Here is a photo I took while I was there. Photo taken from passenger side.
On my trailer the gate valves face the passenger side, and are physically on the passenger side of the trailer, while the actual pull/push handles are on the driver's side of the trailer. The cable goes from the handles, all the way across the trailer, and then does a 180-degree turn before connecting to the gate valves. Utterly moronic design; whoever came up with this needs to be punched in the face.
The one unexpectedly nice thing I did find under there is heating elements under the grey and black water tanks; on most trailers that have tank heating, the heating is only in place for the fresh water tank, because you can pour antifreeze into the other two tanks (to prevent them from freezing). That was a nice find.