A method of cleaning permeable, hollow membranes is disclosed. In one embodiment, the membranes are immersed in a liquid suspension. A pressure differential is applied across the walls of the membranes. During filtration, liquid suspension passes through the walls of the membranes to be drawn off as permeate, and at least some solids are retained on or in the membranes. The steps of cleaning include: applying a cleaning solution to one side of the membrane walls; applying a pressure differential across the membrane walls to cause flow of the cleaning solution through the walls from the one side of the membrane walls to the other side of the membrane walls; and, applying a reverse pressure differential across the membrane walls to cause flow of the cleaning solution through the wall from the other side of the membrane walls back to the one side of the membrane walls.