I mix my star san up in a gallon plastic jug, then pour it into the vinator till it is half full.
I use my vinator by placing it the sink, so if yours is on a bottle tree I would use less.
If you meant how much of the actual chemical goes into the small volume of water in a vinator, then it is hard to say as 2 Tablespoons (1oz) treats five gallons. Maybe like a quarter of a teaspoon or about 6 drops???
profallout says he uses a Tablespoon, but man, thats enough for two and a half GALLONS.