Leviticus 6:11

And he shall put off his garments, and put on other garments, and carry forth the ashes without the camp unto a clean place. This duty was afterward performed by such members of the priestly family as were excluded from officiating at the altar by some bodily defect, Leviticus 21:16. During the wilderness journey some clean place outside of the camp could be used for the ashes from the altar of burnt offering; when the sanctuary of the Lord was in the Temple at Jerusalem, a place outside of the city was chosen.