As a rule, my routine is that I drink as much as I want/need upto 3hrs before weigh-in, then I take in no liquids at all. By the time I get to weigh-in time the tank has run dry!!
If my mouth gets dry during the 3hrs, I take a drink of water, swill, and spit out again.
I know it probably makes no difference whatsoever, but it is a routine I have for myself and I always do the same.