My buddy has a stove in his garage that he let me use. I boiled it in a large round pot. More round and not as tall as the stainless ones used for frying turkeys. I put about a cup of Oxy Clean, Borax and A&H Super Washing Soda mixture as the pot was coming to a boil. It took a couple of 1 1/5 hour boil and clean repeat steps. I used a little pressured water to help out with the process. It was just a focused stream from a garden hose.
The next day I used 40 volume peroxide from a beauty supply store to get it white. I used a large syringe to apply the peroxide. I got a cheap 3 pack used for administering oral medication to farm animals. It worked like a charm.
My rookie mistake was not thoroughly cleaning the pot before I started boiling. I introduced contaminates (small black flakes) onto the skull and gave it an overall grey color from my first boil. I did a second boil at home with the same whitening mix as before but my water level was a couple of inches over the skull this time. It removed some of the chocolate color from the bases as a result of the second boil. After that the skull looked a lot more like I had expected. The second round of 40 volume peroxide made it white as snow.