Or HaChaim on Exodus 30:19/אור החיים על שמות ל׳:י״ט

1 את ידיהם ואת רגליהם. "their hands and their feet." The two words את were not really necessary. The reason the Torah wrote the word את each time is to tell us that washing of the hands without washing of the feet at the same time, or washing of the feet without washing of the hands at the same time did not accomplish its purpose. In other words the word את really means עם. The source for our explanation can be found in Zevachim 19 where we are told that the priest had to sanctify hands and feet simultaneously.