Is it sufficient to pour water over the body when performing ghusl for janabah, or is it necessary to pass the hand over the back (or anus) to ensure that the water reaches it?

In ghusl (ritual bath) for janabah (state of ritual impurity), it is obligatory to make water reach all over the outer surface of the body, including the anus and the area between the buttocks, as well as parts of the body that are usually concealed, such as the navel, under the throat, and the armpits. The Sunnah is for the person performing ghusl to begin by washing the hands and any impurity on the private parts, then perform wudu' (ablution), then run water through the roots of the hair and pour three handfuls of water over the head, ensuring that water reaches all folds of the body, and then pour water over the rest of the body three times with rubbing. The obligatory elements are the intention and making water reach all parts of the body, and that the body be free from impurity. It is permissible to wash the private parts and the area between the buttocks before wudu' and then make water reach the rest of the body.