Actually, because I am cursed with firm curds no matter what I try, there was very little whey expelled during pressing. As in maybe a couple of tablespoons in the first few minutes, a couple of drops on second press, and none on third press. Not a drop.
"Milling curds" I just picked up out of the recipe books. That's what they call breaking up the curd matt that formed while draining. My curds were matted into the shape of my funnel, so I dumped them into a bowl and broke them up with my hands to mix in the salt.