For my first go-through, I use 1 tablespoon of Dr. Bronner’s Castile Soap for every quart of almost (but not) boiling water while filling my machine’s tank. On the second go-through, I use a 50-50 mix of white vinegar — anyone surprised? — and almost boiling water, plus 20 drops of lavender essential oil and 10 drops of tangerine, lemon or grapefruit essential oil, for fragrance
