I just did mine last weekend,i took mine off and used a large screw driver and a hammer to break up the core and then a larger pry bar type screw driver once i got further into it.Dumping it out many times as i went along.
Word of CAUTION: Do not breath the dust that comes out of it or leave it where any pets will get to it,nasty stuff.
Do it away from any nice vehicles, the powder/ dust scratches paint very easily.