Abstract: A cathode (10) surrounding an anode (14) stands on the bottom (11) of a tank (12) that can hold a varying volume of liquid (25) for electrolytic processing. A pump (18) circulates liquid from a drain (17) outside the cathode into a space between the cathode and anode; and although liquid can drain from inside the cathode back into the tank under the bottom of the cathode, the flow rate of the pump is larger so that the pump fills the cathode to overflowing, independently of the level of liquid in the tank. This allows widely varying batch sizes to be processed in a simple and inexpensive way; and it ensures that when tank (12) is drained, liquid (25) within cathode (10) also drains.