A screening apparatus that includes a strainer element used for the purpose of retaining particulate while permitting the passage of a liquid through the strainer element, a support structure for the strainer element to enable rotation of the strainer element between opposed 180 degree positions, and a control member coupled with the strainer element for controlling the rotation of the strainer element. The strainer element, in both opposed positions thereof impedes any particulate while permitting the passage of a liquid. The control member is constructed so that, in a first state thereof, the rotation of the strainer element is periodically controlled to rotate the strainer element between said opposed 180 degree positions, and in a second state thereof, inhibits rotation of the strainer element.