So with the buttermilk.
Drink it or soak in it, cold?
Warm it to body temp in a pan of warm water and douche with it. Make sure the buttermilk is cultured buttermilk because it is the natural bacteria that restores the balance in the vagina.
P.S. A friend of my wife had a yeast infection so severe she was hospitalized. After they tried every anti-fungal known, someone mentioned the buttermilk douche. It worked.