I knead it in my hands in between rinsing it in cold water, kneading it under water a bit, too. It isn't perfect, but gets most of the water out. I knead the salt into it at the end, which seems to get just a bit more out.
I culture my cream with store bought buttermilk and it results in butter that is very nicely spreadable right out of the refrigerator. Higher yield that way, too.