There are many variations to this method. So choose what works best for you.
You will need to DILUTE approx. ¼ cup of Apple Cider Vinegar into 2 cups of warm water. (Your standard water bottle with a hole poked in the lid should do the trick).
After you have washed your hair, used a deep conditioner and rinsed well, you will pour and massage the diluted ACV mixture all over your hair. Avoid your eyes, as it will burn. The ACV is very acidic, so if you have used too much, you will know right away, because it will sting a bit at which point you should make a mental note for next time, and continue to massage the scalp.
You should focus carefully on the hair at the nape of the neck, as that is where a lot of build up will linger. Rub individual locs in between your fingers trying to rid each loc of any buildup that may be hiding inside. After about 10 mintues, or as long as it takes you to focus on problem areas, you can rinse your locs well.
Sometimes, I use the ACV rinse after my shampoo, and before my deep conditioner, so that the conditioner will leave my locs feeling moisturized and not so dry.
Apple Cider Vinegar rinses are used to remove build up that occurs from using or over using creamy hair products and shampoos. This rinse is particularly important for loc-wearers because you are not brushing your hair, you tend to see the build up in your locs. Not cute. ACV rinses also stimulate the hair follicles to promote healthy hair growth and close the cuticles so that moisture is retained for longer periods of time and give the hair a healthy looking sheen.
Apple Cider Vinegar is over 100x more acidic than your hair. It is potent stuff. Overuse can cause breakage, split ends and brittleness. Doing an ACV rinse a month or even every other month should be more than enough to reap the benefits.