Well? It LOOKS easy on paper!
Interactive parts catalog lets us look through the walls!
https://catalog.winnebagoind.com/menu/Parts.htm
What it DOESN"T do is let us look at drain and water supply on one view!
So maybe some of what seems to be there to compare to what you see?
Click these for better view or go direct for the whole picture!
Get it from right side to drain by remove panel? Then if you can see the end of black tank, use it to slide wire to right on top of tank.
Second pic is of tank to right of first pic?
Are you a good snagger? Can you get the wire to float along the first tank top and then drop down in the space between the wet bay panel and the tank? There is about a 8-12 inch gap shown. Can you get an arm up under the panel to avoid having to remove a ton of fittings/lines?
Maybe a blind sow looking for some luck??
Easier to remove panel at drain than panel at wet bay, due to lots of lines there? Maybe just a few screw and the line flexs enough to get it done?
But what is the funny slot? NOT a mail drop , I hope!!
Just some ideas to consider for right or wrong, the idea is cheap!