Washing a limb means that at least 2 drops of water must flow over that limb . if the limb is
simply moistened by rubbing a wet hand over it , or if only 1 drop of water flows over it then it
will not be considered washed and the wuzu of ghusl will not e considered complete.
(maraqil falah ma' Hashya-tut-tahtawi, P57 - Fatawa-e-Razaviyah, V1 P218, Raza Faundation)