A flexible bag (1) that is partially filled with a basic liquid solution (21) has a first end closure (3) from which a mixing tube (7) extends that is provided with a frangible closure cap (8) and a terminal (9) that is suitable for the connection of a container (22) of active substance (23) to be mixed with the basic liquid solution (21) and a second end closure (5) from which two dispensing tubes (12, 13) extend that are provided with respective frangible closure caps (14, 15). A first dispensing tube (12) has a terminal (18) of the press type and a second dispensing tube (13) has a terminal (19) of the screw type (FIG. 1).
