Easiest thing to do - is the hide still on it? If so, dunk it in a bucket for a day to soften the hide, then cut/pull the hide off (wear rubber gloves), it's not too bad after only a day. After that, strap it down to an upside down pallet or something similar and hit it with a pressure washer if you have access to one - it will be clean in a fraction of the time it takes to boil one. After that search skull whitening online and go from there. I've done hundreds of skulls this way.