Komentarz do Kapłańska 8:6

AND HE WASHED THEM WITH WATER. It appears likely to me that Scripture tells that he [Moses] washed all of them, but nonetheless it was not done to all of them together. Rather, he washed Aaron and clothed him with his garments and anointed him, and afterwards he washed his sons and anointed them.

וירחץ אותם במים, “he immersed them in water.” Nachmanides writes that he believes that most likely Moses immersed all of them (Aaron and his four sons) in a ritual bath; however, he did not immerse them in such a bath simultaneously, but he first immersed Aaron and then dressed him in the appropriate priestly garments; anointing him. Following this, he performed the same procedure on each of Aaron’s sons.