Abstract: An apparatus for mixing a bathing liquid into shower water, of a type that includes a reservoir assembly for holding the liquid and a mixer coupling connected between a water outlet and shower head to mix bathing oil from the reservoir with water flowing towards the shower head. The reservoir assembly includes a reservoir that can hold a small quantity of bathing liquid, a container which can hold more than the reservoir to repeatedly fill it, and a housing that pivotally supports the container to flow bathing liquid into the reservoir until the liquid reaches the level of the opening in the container. The mixer coupling includes a venturi to pass shower water and draw in bathing liquid, a chamber between the venturi inlet and the shower water entrance, an air vent leading to the chamber, and a diaphragm freely movable in the chamber against and away from the air vent to permit the outflow of liquid from the coupling when the shower is turned off.