I would certainly wash them with water (soap optional) until they LOOK clean, before sterilizing. That way there won't be germs hiding inside clumps of dirt, manure, feathers, etc.I tried looking this up and all I could find was was with soap and water. Is the best way just soap and water or is there a better way of going about that?
Sunshine can also kill germs, so getting them visually clean and then sitting them in the sun for a few days might be another option.