This is part of a discussion of whether a cat can drink a potion or not... I assume the other guy was as confused about it as I was, since he suggested the cat could lap up just about 10% of it to be able to drink it all in one round.
Potions are
1 use items. Not 2, but
1 use. That is the easiest way to keep up with
how you can use a potion. You would be unnecessarily complicating things by nit picking any details about something as minor as drinking a potion.
Size of the creature doesn't matter. A colossal creature doesn't need
more than 1 ounce for a potion to work. If you want the potion to work for the cat, rather than claiming that the cat doesn't drink an ounce in 1 round, just claim the cat drinks the entire ounce or hand wave it and assume whatever it drinks in 1 round is good enough and the rest is wasted. Otherwise, you are rules lawyering for no good reason other than to either screw over the cat by not making the potion work, or you're trying to bend the rules and get a potion to work more than once.
Anything other than this would be a house rule. Tasting a potion to identify it is the equivalent of touching your tongue to the liquid or smelling it. Neither of which is going to reduce the "1 ounce" enough that it wouldn't still be considered to be an ounce.
I assume you don't drink alcohol or you're underage since you didn't know how much an ounce is.

But a good way to think about this is to consider this; if I can get drunk by drinking a shot of vodka (a shot glass is considered 1 ounce), will I not be drunk if I don't lick the glass clean? Or if a drip of it falls on my shirt as I'm taking the shot, does that mean I won't get drunk because I didn't include that drop? It won't really make a difference. Just think of a potion as being the same thing.