If the universe contains all matter and energy, where do the additional “drips” come from? Even if you found a source of addional “drips”, your bucket is a fixed volume. An expanding universe is a growing volume. Accelerating the rate of expansion means that the force causing the expansion must be increasing, to compensate for the increasing volume. Perhaps there is something surrounding what we perceive as the universe, that exerts an attractive force, pulling the universe outward, in all directions.