The correct answer is C) the cage must be free of rubbish or the ball may not seat properly. For the automatic lifeboat drain to operate properly, the cage or housing around the drain mechanism must be clear of any debris or obstructions. If the cage is blocked by rubbish, the ball float that is designed to seal the drain may not be able to properly seat and close the drain opening, preventing the water from draining out effectively. The other answer choices are incorrect because they do not address the key requirement of keeping the drain mechanism cage clear. Turning the lever counterclockwise (A) or removing the cap (D) are not necessary for the automatic drain to function, and an automatic ball check (B) is not the critical factor - the cage itself must be unobstructed.