When my powdered foundation compacts are almost all empty in the center but still have a little around the edges that are hard to get to, I've been sticking them in a drawer, not knowing what to do with them.
Until recently, I found a little tin, that I've taken a sharp knife and gotten out all the excess powder that's still in the compacts and combined it all in a bowl to crush and then put in the tin with a lid.
So now, I can use a make-up brush and use the excess powdered foundation as I normally would, tossing out all the old compacts afterwards, thus cleaning out my drawer and none of my powdered foundation goes to waste, either.
By T. H.