The invention provides an apparatus and method for handling a solid/liquid mixture, for example for conveying fish immersed in a fish/water mixture. The apparatus has a receiving chamber (12) to receive the mixture through an inlet valve (16) when the chamber is subjected to low pressure, and to discharge the mixture through an outlet valve (18) thereof when pressure in the chamber is increased. A quantity sensor (73) is responsive to a predetermined quantity of mixture within the chamber (12) to isolate the chamber from low pressure when the predetermined quantity is reached. The inlet valve (16) is positioned adjacent an upper portion of the chamber above a maximum upper level of mixture within the chamber, and has seat clearing structure to clear the inlet valve seat of solids when flow therethrough ceases. An inlet flow sensor (34) is responsive to inlet flow of mixture through the inlet valve and raises pressure in the chamber when the flow therethrough stops, to provide time for solids to clear the inlet valve (16) before closure thereof. The quantity sensor (73) also has a mode selector for selecting mode of operation of the apparatus which is responsive to quantity of mixture and controls pressure changes within the chamber. A valve/switch which controls actuation of controls for changing pressure within the chamber is magnetically responsive to flow sensors (34, 92) disposed within inlet and outlet ducts to permit actuation of the valve/switch without mechanical contact therewith. This isolates the valve/switch from contamination with the mixture in the duct and vice versa.