Does scooping water from a large vessel using a small vessel, in such a way that the used water from the hand falls back into the large vessel, render the ritual bath (ghusl) insufficient?

The ghusl (ritual bath) is valid and sufficient. If the water used is pure (tahoor), then the matter is clear. If it loses its purity, then a small amount that falls into the vessel from which water is drawn is excused. A small amount of used water falling into (pure) water is forgiven. The proof for this is that the Prophet (peace be upon him) and his companions used to perform ablution (wudu) and ghusl from vessels into which splashes of used water inevitably fell.