IMO it is better to take out a portion of the slurry - heck, it only takes a minute to dump in clean, sani mason jar, and measure out the appropriate amount. Also, the bruno hefe - the old yeast and protein hop resin on the sides if the fermenter - you dnt really want that to dissolve back into your beer. I think you make better beer by measuring out the slurry and pitching into a clean fermenter.