1)
What are the connotations of "Vayirchatz osam ba'Mayim"?
1.
Rashi (in Tetazveh, Sh'mos, 29:4): It means that he Toveled them in a Mikvah. 1
2.
Ibn Ezra: It means that he washed their hands and feet from the Kiyor.
1
Oznayim la'Torah: In other words, Aharon and his sons Toveled in front of him ? like a Ger is required to Tovel in front of Beis-Din (See Oznayim la'Torah). And Moshe was considered a Beis-Din ? even of seventy-one. See Sanhedrin, 16b.