product from entering the air supply line 74 to any significant extent another check valve 80 in the discharge line 60 downstream from the pump 48 prevents air from the supply pump 72 from entering the discharge pump 48 the air from pump 72 can also be utilized to dry out the discharge line 60 and the augmentation chamber 70 after each batch of product has been prepared and distributed preferably the entire system is flushed prior to such drying action by simply allowing the appropriate liquid carrier 34 or 42 to pass through the chamber 16 pump 48 and discharge conduit 60 without the introduction of any additive or foaming agent from the supply hoppers 10 12 respectively when the truck 68 arrives at the dispensing station as illustrated in the drawing the contents of the container 66 may be weighed using a scale 82 that inputs the resulting information to a computer 84 such that when the weight of the contents is known the computer 84 can then appropriately signal the rest of the system to release only the appropriate amount of additive from hopper 10 and foaming agent from hopper 12 for the particular job thus for each truck that arrives the system has the ability to adjust itself to supply a batch of additive in accordance with a pre established concentration schedule and accordingly adjust itself to supply the amount of foaming agent necessary to achieve appropriate.