I do my ACV rinse last. I prefer to leave the acidity in my hair rather than rinse it out with distilled water since I like the fact that the ACV helps the hair cuticle lie flat and thus helps in locking in the moisture. I mix my ACV rinse at the time I'm going to use it. I can't tell you how much (sorry), I just pour...making sure not to put too much coz too much acidity can be bad for your hair (according to the Pantene website). I argue that a drop is better than none so I put very little. If you are more comfortable with measurements, here's a recipe for a rinse...more like a spritz. But I don't see why you can't just add the amount of water and make it a rinse:
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Essential Oil Vinegar Rinse
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2 tablespoons (8 teaspoons/40 ml) apple cider vinegar
20 drops lavender oil
20 drops rosemary oil
10 drops geranium oil (or lemon oil if hair is oily)
Rain or distilled water
1 teaspoon vegetable glycerine [/list]
Mix essential oils and vinegar together in a 300ml spray bottle. Fill up with purified or rain water. Shake well before use.
To use: Rinse the hair after shampooing then spray thoroughly with the vinegar rinse.
Don't rinse out.
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Source: http://www.neryspurchon.com/recipes/haircare1.html
HTH