Typically a traditional liquid rheostat consists of a steel cylinder (the negative), about  in size, standing on insulators, in which was suspended a hollow steel cylinder. This acted as the positive electrode and was supported by a steel rope and insulator from an adjustable pulley. The water pipe connection included an insulated section. The tank contained salt water, but not at the concentration that could be described as “brine”. The whole device was fenced off for safety.
Operation was very simple, as adding more salt, more water or varying the height of the centre electrode would vary the load. The load proved to be quite stable, varying only slightly as the water heated up, which never came to boil. Power dissipation was about 1 megawatt, at a potential of about 700 volts  and current of about 1,500 amperes.
Modern designs use stainless steel electrodes, and sodium carbonate, or other salts, and do not use the container as one electrode.
Systems with frequent starting may include water circulation to external heat exchangers. In such cases anti-freeze and anti-corrosion additives must be carefully chosen to not change the resistance or support the growth of algae or bacteria.