Tell us what the fluid tastes like. If it is sweet, then it is anti-freeze. If it kind of tastes burnt butteryishy, then it is motor oil. If it tastes really really bad then it is ATF. If it smells and tastes like paint thinner, then it is brake fluid. If it tastes bitter, then it is windshield wiper fluid. And if it smells really really bad, don't bother tasting it because it is gear oil.
Not that I go out of my way to taste automotive fluids, but working on old cars for the past 40 years, you eventually get a little of every kind of automotive fluid in your mouth at some point.