^ LOL. PIZZA! Seriously now.... How about something that melts/corrode part of the bucket? or...... nothing?
@Nikotsumi HOLD IT~! , You put acid, to make a hole. By that definition, you have placed something in the bucket, to produce a hole, which in turn makes it lighter. CASE CLOSED guys. B-)
This is actually a trick question! Lighter can be interpreted as ''lighter in weight'', but also as ''lighter in brighter''. The answer is: A torch.