I hold the siphon tube just above the unhatched cysts in the bottom of my pop bottle hatcher.
Another thing I learned was to rinse the hatching bottle out in very hot water, but not to clean it.
Soon, a film builds up on the sides so that when siphoning, most of the hatched cysts floating on the top, adhere to the sides of the container, making it easier to siphon right down to just above those unhatched cysts on the bottom.
I then rinse the nauplii in fresh water (not salt water) before using them or placing them in the growout containers.