Abstract: A apparatus for mixing separately contained media such as would be used in a wet abrasive blasting operation comprises a receptacle (10) for a liquid/abrasive medium, a receptacle (11) for a liquid, and a delivery line (20) along which pressurized fluid is adapted to be fed. The receptacles (10,11) communicate via pipes (22,23) with the delivery line (20) so that the liquid and the liquid/abrasive medium are entrained by the pressurized fluid. The receptacles communicate with each other via a hole (14) to balance the fluid pressure system between them and a means (15,19) is also provided to deliver pressurized fluid into at least one of the receptacles (10,11) in order to substantially balance the fluid pressure system between the receptacles (10,11) and the delivery line (20) and to facilitate outflow of the liquid/abrasive medium and the liquid into the entraining fluid.