We NEVER use our blue tote tank for black water, only gray water.
Because it takes much longer to fill a 25 gallon black tank, than a 25 gallon gray tank.
The two of us can easily go 2 weeks before we even get close to needing to dump the black tank, when we dry camp.
Since you don't list what you're pulling, I have to guess that it's a hybrid.
Pulling a HTT/TT with a gasser, will always put you in the 8-11 mpg range.
Pulling with that small v-8, will probably put you in the lower end.
everyone pulling with a gasser, gets that mileage range.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC