For 500 ml. (1/2 litre)

Mix directly in an upcycled bottle (preferably larger than the quantity of liquid):

½ litre hot water
1 tsp sodium bicarbonate
1 tsp washing soda
2 tsp savon noir

A few drops of essential oil(s) of your choice for scent and individual qualities (i.e. grapefruit, tea tree oil, lavender…)