Hi Scott,
It was the old powdered detergent called BIZ. I found it at Wal-Mart.
It works wonders in removing the meat off of skulls, bones, etc. A skull collector friend of mine has used it for years. Youput the skull on a rack inside a pot full of water, add BIZ ( 1/2 a cup for a small skull) and bring to a slow boil, then turn down heat and let it barely simmer until the meat is loose. Remove skull, clean excess meat off skull then do it all over again with fresh water and another 1/2 cup of BIZ. in a couple of hours the skull will come out clean and white. Boiling hard will usually crack the teeth and can crack the skull, so do it slowly.
A trick to make the skull look nice and last longer is to put Elmers wood glue on you fingers and rub it into the skull's surface and the teeth. This keeps the teeth from coming loose and makes the skull easier to clean (dust) as well as weatherproofing it.
Dave
