When did Moshe, Aharon and his sons all wash from the Kiyor?
Rashi: On the eighth day of the Milu'im exclusively, when they all served as Kohanim in the Mishkan. 1
Moshav Zekenim (citing Zevachim 19b): Even though they did not all serve at on the same day 2 , the Pasuk is coming to teach us that the Kiyor must hold enough water for four Kohanim, corresponding to Moshe, Aharon and two sons. 3 In any case, Moshe needed to wash during the seven days of the Milu'in.
Riva (39:32): as Rashi explained in Zevachim (19b) - Moshe was Kohen during the first seven days of the Milu'im, but not on the eighth. In fact, it is a Machlokes Tana'im. Refer to 40:31:2:1 and note.
Shitah Mekubetzes (19b): And the reason that we include Moshe, even though he did not serve after Rosh Chodesh Nisan, and not Nadav and Avihu, who also served on that day, is because "u'Vanav" refers to only two of his sons. Ma'asei le'Melech (Hilchos Bi'as Mikdash 5:13): Rashi here goes according to Rebbi in Zevachim 115b, who holds that Nadav and Avihu became Kohanim at Sinai and 'Banav' includes only them. Avi Ezri (ibid.): Since it was already decreed that Nadav and Avihu shold die, they are not counted. The Rambam there mentions Aharon, Elazar and Isamar. His text in the Gemara reads "Aharon u'Vanav" (30:19, the command to make the Kiyor), so he was forced to include Pinchas - which follows the opinion in Zevachim 101a, that Pinchas was already a Kohen.
What are the implications of "Verachatzu Mimenu Moshe Aharon u'Vanav"?
Zevachim, 19b: It implies that the Kiyor must always hold enough water for four people to wash from it - Moshe Aharon, Nadav and Avihu. 1
Why do the Kohanim need to wash their feet, seeing as they are not used for the Avodah!
Moshav Zekenim (citing R. Yeshayah); They wash their feet based on the Pasuk in Koheles 4:17 "Sh'mor Ragl'cha Ka'asher Teilech el Beis ha'Elokim".
