Converting Black Tank into a Grey Tank Overflow?

[mpierce]

"As a reference, on my 91 WB40, the factory specs say fresh water is 137 gallons
and the grey and black water tanks are both spec'ed at 100 gallons.
So in the end result when dry camping, you'll probably run out of fresh water first
before you fill either tank.
So tying the tanks together seems somewhat superfluous."

Unless you have a portable bladder, and go and get water, and bring it back to the fresh water tank, then it would help out.