A process and apparatus for periodically dumping liquids in an installation, in which liquids are recycled or otherwise accumulate dissolved and/or suspended contaminants, which process and apparatus makes use of a container for a liquid which is alternately filled and drained during operation of the installation, resulting in changing weight or buoyancy of the container or level of a float in the container, which actuates a dumping valve when a given critical weight, buoyancy or float level is exceeded or reduced.