Welcome to the forum. I have the rockwood version (hw277) and only use the gray tank (we do not use the toilet- did not want to mess with it). Well, when the gray is full, it backs up into the shower. Don't think there is any way for the black other than to look in it from the top (i.e. peek in from the toilet, the tank is right below). Maybe someone else has a better way for the black. The pullout dinette, we do not use any extra support, it holds all of us (we are not too slim either). Did have an issue with the dinette bed breaking (pulled one of those little strips of wood holding the table in the bed position right out of the bench). We did add extra support to those little strips.
HTT: "EscapeII" 2016 Shamrock 23WS (current)
PUP: "Escape" 2010 Rockwood HW 277 (gone)
TV: "Bruce" 2011 Dodge Durango V8 Hemi Crew
Just us gals (me, Sis and our daughters)
Traveled 19520 miles and 209 nights in 7 years and counting