Yea soaking it N Bleach a couple times will do it, I've never tried it But i think it would look BadA$$ if u can tape off the tusk r something to protect it from getting Bleached when u soak the skull. The skull will B white But the tusk will B dark & ruff looking, just an idea.
If you wanted to accomplish that, you just soak it in plain water for 3 days then pull all the teeth. Bleach everything, then re add the teeth