John Gill Commentary Exodus 40:31

"And Moses and Aaron and his sons washed their hands and their feet thereat;" — Exodus 40:31 (ASV)

And Moses, and Aaron, and his sons, washed their hands and their feet there. This laver was for the priests, and Moses, officiating as a priest, washed in it, with Aaron, and his sons, whom he was now about to consecrate to the priest's office, and invest with it by offering sacrifice for them; Jarchi says this was on the eighth day of the consecration.