I don,t use salt as I prefer it plain, but mum puts a bit of salt to taste. I do not wash it, I just drain the buttermilk into a jug, then use a couple of wooden spoons and keep squeezing it after that I put it into a little pot and push down with a wooden spoon and drain of a bit more. My 12 year old daughter often does this bit as she enjoys it. The dogs love the butter milk but I put it in a quick recipe for butter batch rolls which I got from an Aga cookbook (mine's a rayburn though, my £1 bargain).
Many, many years ago, I worked at a social history museum and we did that there, only we used a glass butter churn instead of a kenwood, everything else was the same though.
I can photograph what I do if it is any help to people.