PURPOSE: To simplify the structure of a container itself and discharge the liquid in the container without moving the container and without necessitating a power source by discharging the liquid in the container by the syphon action by using a U-figure pipe.

CONSTITUTION: The container such as parallelepiped is arranged in tilted form by an angle θ with respect to the diagonal line on the bottom surface. In treatment, liquid is poured to a lower level 8. When liquid is discharged, a U-figure pipe 9 is arranged, getting-over the wall surface of the container 1. The arrangement position is the lowest position on the peripheral wall surface according to the tilt angle θ. Water or treating liquid is additionally poured. When the liquid level increases and reaches a level 10, a syphon effect is generated in the U-figure pipe 9. Then, the additional pouring is brought into stop, and liquid is discharged by the syphon action.