View of a "foot washing stone" that was discovered in Nahum Avigad's excavations in the Jewish Quarter of the Old City of Jerusalem.
This solid one-piece stone was carved out with a "heal rest" left protruding in the center of the stone. In the bottom is a hole through which a liquid could drain out.
To wash one's foot, the standing person (maybe sitting) would place their heal on the raised center piece. Then a servant would pour water over it, cleans the foot, and then use a towel to dry it. The process was repeated with the other foot.
Obviously the lower status person would wash the feet of a higher status person.
Note that Jesus washed the feet of his disciples (John 13) and see 1 Tim 5:10—"washing the feet of the saints."