I stopped using the filler except for VERY special occasions because it's just too messy! Pixel would end up with it all over the house
I stuff his kongs with this now instead: Stuff'n Snaps
http://www.petplanet.co.uk/shop_dev/assets/extra_images/6370/10_kong_snaps_unpacked.gif
He loves them and they are A LOT less messy, so mommy loves them too