A medical fluid supply device including at least first and second fluid containers which are arranged to be mutually displaceable, at least first and second selectably openable fluid communication pathways associated with the first and second fluid containers and at least one selector switch assembly for selectably opening the first and second selectably openable fluid communication pathways, mutual displacement of the first and second fluid containers changing the amount of fluid in at least one of the at least first and second fluid containers in accordance with a state of the at least one selector switch assembly.
