How do I prevent the pump sucking in air?

If a pump operates without water, it can break down. Always fill a self-priming pump with water before switching it on. Alternatively, you can install an anti-leak check valve, either at the pump or at the bottom of the suction pipe. If you install a valve at the bottom of the suction pipe, the pipe will always be filled with water. In that case, you must be careful if frost is forecast. Also remember not to damage the anti-leak check valve by turning it too far by screwing a fitting in too far. The valves have checks inside them so you cannot screw fittings with long threads completely into them. If you screw them into too far, the valve will not close and the pipe will empty.