ויקרא יג:נח פירוש: רש״י, רבנו בחיי וחזקוני

וסר מהם הנגע IF THE PLAGUE BE DEPARTED FROM THEM — if when they washed it at first by the order of the priest (Leviticus 13:54), the plague departed from it entirely (cf. Sifra, Tazria Parashat Nega'im, Chapter 16 10),

וכבס שנית, “it shall be immersed in a ritual bath a second time.” The second time in order to purify it, whereas the first time was in order to remove the residue of the plague.