A valve for use in changing automatic transmission fluid, obviating the need of removing the oil pan. The valve is interposed in the hose line connecting the transmission fluid outlet to the cooler inlet. The valve has an interior, control slide to allow, in its first state thereof, the normal flow of the fluid from the transmission to the cooler, and, in the second state thereof, diverts the flow from the transmission to a drain outlet for deposit of the old oil in a container for eventual disposal. In using the valve, a desired amount of old oil is drained, and simultaneous therewith new oil is added to the transmission. The control slide is held in its first state by a spring, and is held in its second state by a hollow push-rod connected to the dispensing outlet of a container, the push-rod and its associated mounting element allowing for the through-flow of the old oil directly to the container.