carry the fresh water, will make undetectable difference in your fuel mileage
go with near empty freshly chemically charged holding tanks
IF they get full before the ballon fest is over pay for the pump out
if they don't get full, your $25 ahead
i pay $30 where i go to dump
and i have drive there, $25 pump out is a bargain, your going be there, do you want the hassle of moving just to dump someplace free
IF you need more water buy it, but start out with full fresh water, ALWAYS when dry camping