Welcome Jack Joy. The tank indicators that Gene describes are on the later models, like 1996/1997 and later. Your vintage would have had them on the stove hood, but your particular coach doesn't have them. Actually, all the models T-2251 and shorter didn't have monitor panels then. Only the longer coaches had them.
If you were to go back a model year, you would notice that your 2052 was actually considered a "Saturn" model instead of a "Solaris" model. The Solaris models traditionally were the longer coaches (23'/T-2362 and longer) whereas the Saturn models were the shorter ones. The Solaris models had more features than the Saturn, I'm not sure why. They must have figured anyone who bought a longer one would use it more and for longer periods over someone with a shorter one. In 1995, in honor of the 30th anniversary (and for this year only), they decided to make everything a Solaris model, though the coaches under 23' still had less features like the former Saturn.
I'm not sure why they still included that schematic for the tank indicators in your book. I have seen other cases where they did though. Maybe there is pre-wiring for them somewhere, I don't know.
Since you have rear twins, I'm guessing your fresh water tank is underneath one side. As a result, it's probably smaller than the one in the 2053 would be under the big bed. You still should be able to pick up the bed and see the tank to know how full it is. The black tank can be measured partly with judgment based on use and partly based on looking down the toilet with the valve pulled open. The gray tank is the most difficult, and will fill up the quickest, so you'll just have to try to remember how much you've used. It will get easier with experience too, of how long you can last.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR