To easily wash a concentrate container by disposing a reservoir between a dilute liquid source and a mixing tank so as to be spaced apart from the diluted liquid source by a predetermined air gap so that diluted liquid is received from the reservoir to send it to a container station through a concentrate outlet port.

If a concentrate container 14 is placed in a container station 12 and unsealed using an unsealing device 22, a concentrate is discharged from the container 14 and flows into a mixing tank 32 so as to be mixed by a mixing device 40. And when a sensor 54 senses an increase in volume, a control device 58 determines the total volume of diluted liquid based on the information so that the diluted liquid is supplied to a reservoir 62 by means of a distribution device. A first part of diluted liquid overflows from the reservoir 62 into a tank 32, while a second part thereof is held in the reservoir 62 to a washing process. And after diluting operation, a flowable part of the concentrate is discharged and after introducing the second part of diluted liquid, a pump 88, as washing device, is actuated to wash the container 14.