the assembly comprises a pair of substantially identical unitary plastic molded units , each unit having a tubular stem formed with a piston at one end and a nozzle head at the other . each unit has a female snap - type connector facing to one side and spaced therefrom a male snap - type connector facing to the same side , the molded units being disposed side - by - side with the male snap - type connectors snappingly received into the female snap - type connectors of the respective stems .