This is the way you will do it: Sprinkle water of absolution on them; have them shave their entire bodies; have them scrub their clothes. Then they will have purified themselves.
"Have the Levites place their hands on the heads of the bulls, selecting one for the Absolution-Offering and another for the Whole-Burnt-Offering to GOD to make atonement for the Levites.
The Levites have been selected out of the People of Israel for my exclusive use; they function in place of every firstborn male born to an Israelite woman.
Every firstborn male in Israel, animal or human, is set apart for my use. When I struck down all the firstborn of Egypt, I consecrated them for my holy uses.
selected out of the People of Israel, and I have given the Levites to Aaron and his sons to do all the work involved in the Tent of Meeting on behalf of all the People of Israel and to make atonement for them so that nothing bad will happen to them when they approach the Sanctuary."
The Levites purified themselves and scrubbed their clothes. Then Aaron presented them as a Wave-Offering before GOD and made atonement for them to purify them.
They can assist their brothers in the tasks in the Tent of Meeting, but they are not permitted to do the actual work themselves. These are the ground rules for the work of the Levites."