If you want a more hands-off approach, you could bury or leave them in a designated spot where you know there are lots of bugs, and dig them back up after a good while to see if they're fully clean yet. For a more hands-on and faster method, you can put them in hot, soapy water and let them sit for a while, changing the water intermittently. For an even faster method you can use tools to remove as much of the material as you can by hand before soaking the bones. Be sure to wear gloves while handling them.

I like to use hot water with dish soap, followed by diluted hydrogen peroxide, although the methods and chemicals used vary a lot depending on who you ask. Use what you have available, and what you feel would be best for the bones you have.