I have this to pass on to those of you who have hog or bear sculls to clean. All hog sculls leach out for the longest time....this takes time but works great...
After you boil-cut-scrape or rot your flesh off put your scull in a 5 gallon bucket and fill the scull cavities and the bucket until everything is covered with floor dry or kitty litter then put in you attic and forget it for a month or two. Bleach then clear coat.

Drill a hole in the back of the skull, and using a coat hanger shaped like an L, or anything simular mush up the brains and then drain them out....saves time. Don't over bleach as that will make the skull brittle..I use Hydrogen Peroxide as opposed to bleach, but it too can be overdone.

I have been told WD-40 will rid the skull of oily residue.