A sterile device designed to be used with a haemodialysis system for filtration of dialysate during haemodialysis to remove bacteria and endotoxins and produce purified dialysate for the procedure. It may perform secondary safety filtering to prepare on-line substitution solution that can be infused into the patient to compensate for loss of fluid volume resulting from haemodialysis. It typically consists of a plastic housing, containing a hollow fibre membrane, with appropriate connectors at either end. This is a reusable device.