A liquid filtration system according to the present invention comprises a bioreactor; a filter configured to filter liquid passing therethrough; a perfusion pump configured to move liquid between the bioreactor and the filter; a liquid line providing fluidic communication between the bioreactor, perfusion pump and filter; and a bleed outlet provided on the liquid line, the bleed outlet configured to provide means to remove liquid selectively from the system under the action of the perfusion pump. With the liquid filtration system according to the present invention, both the filtering and bleed functions may be performed under the action of a single pump, thereby significantly reducing the complexity and cost of the components required.