How much yeast is typically collected from the primary for reuse?
I usually secondary/cask condition in a corny. Once the corny is filled, the rest of the beer and yeast and trub go into a flask and into the fridge to settle out.
I get anywhere from 1.5-3 quarts of liquid, and that settles into 1-3 cups of thick slurry. I pitch 1-1.5 cups of that thick slurry into my next beer (depending on the OG and how long the yeast has been in the fridge). Using this method has given me very consistent and good results.