a member within a container is reciprocated to vibrate the container contents . a drive unit is releasably connectable to the reciprocating member so that the drive unit can be used for other purposes , such as for driving the reciprocal members of other containers when not required for the container in question . the drive unit comprises a reciprocal output member with a releasable mechanism for drivably connecting the output member with the reciprocal member of the container and a device for removably mounting the container on the drive unit .