Soak them in some Oxy-Clean, Easy Clean, or some One Stepand scrub them good with a brush. You will be really surprised what this stuff can soak off overnight.Wash them again good with a good mixture of the same stuff then sanitize properly with a proper sanitizing solution.
Using the bleach will work but it will not clean the bottles like the above listed oxygen based cleaners will. Bleach will sanitize but is not really that good of a cleaner.If you do use bleach, rinse very, very, very. very well. It is tough to rinse off. Same goes if you use a soap product. If possible, use an un-scented soap product.