Will usually take about two of the small bottles. So, to cover bases, if you are not switching types (DOT 3 to 5 or DOT 3 to DOT 4
synthetic) then no worries, flush until new fluid comes through. Otherwise, you will need to use de-natured alcohol to flush the old fluid, then the new fluid to flush out the alcohol. Anyway, just make sure not to mix the two types.