You will never get the stuff 100% clean, but you don't want to use it right out of the bag. You will have a lot of crap in your tank.
I put mine in a large container with holes and screen on top to prevent flow over, put it out side and had my house sump pump into it for a week.
I still had some dust during my first tank fill. I think when it dries, its gets dusty again, but now as much as when it is brand new and unwashed.