I have 4 of them and have done over 90 batches with them, after a lot of trial and error my process is to dump the collection ball at the end of primary, usually when bubbles through the airlock slow down to 1 or 2 a minute. Before re-attaching the collection ball I always purge it with CO2, then open the valve to collect the later dropping yeast. Depending on the recipe and yeast type, it is not at all unusual for the collection ball to be full to overflowing with yeast sediment and trub after just a few days [the balls hold 750 mL]. Again, depending the recipe I usually dump the ball just before cold crashing and again after [I do a lot of beers with very high percentages of Rye, the sediment from that can be prodigious]. I also save the contents of the ball in a jar in the fridge, even if I don't end up re-using the yeast, the beer sitting on top of the yeast after chilling and separation is perfectly drinkable, although flat.
One thing I can't stress enough is the importance of dismantling and cleaning the vavle body after EVERY batch, do it once and you'll see why I say this.