Bob,
I think the concept as to tank capacities on the '76 models was an excellent
one. I have a 25' Tradewind.
It has a very large fresh water tank - 50 gallons or so, a substantial size
black water tank and a small grey water tank.
You can alway get rid ot the grey water, but the black waste dump sites are
more scarce. Having a large supply of fresh water gives you a lot of
options and a substantial period of operating self contained (along with the
substantial black water tank).
I think this is an excellent tradeoff - giving you long range with a minimum
of weight, and the option of carrying less fresh water if you won't be
needing it.
The grey water tank can fill up fast if you go crazy in the shower or rinse
dishes with lots of water (perhaps like at home). Also, on shorter trips,
if dumping the grey water is a problem, you can always use the plastic jug
to transfer it to the black water tank via the toilet.
I think some of the newer Airstream trailers do not have as large a fresh
water capacity. In my opinion, this is a mistake.
Oliver