A method of concentrating sediment in a water tank involves attaching a vortex inducing device to an opening through the roof of the tank between the central vertical axis and the side walling of the tank. The device has a device inlet which narrows to a device outlet. The device outlet is orientated such that, water flowing out via the device outlet induces a vortex within the pooled water, thereby causing sediment to collect centrally on the floor of the tank.