6 inches-even if you do not know the answer to this question, you can answer it correctly by imagining. if you pour the nss into a receptacle 1 to 3 inch above it, chances are, the mouth of the nss bottle would dip into the receptacle as you fill it, making it contaminated. if you pour the nss bottle into a receptacle 10 inches above it, that is too high, chances are, as you pour the nss, most will spill out because the force will be too much for the buoyant force to handle. it will also be difficult to pour something precisely into a receptacle as the height increases between the receptacle and the bottle. 6 inches is the correct answer. it is not to low nor too high.