Albert Barnes Commentary 2 Chronicles 29:16

"And the priests went in unto the inner part of the house of Jehovah, to cleanse it, and brought out all the uncleanness that they found in the temple of Jehovah into the court of the house of Jehovah. And the Levites took it, to carry it out abroad to the brook Kidron." — 2 Chronicles 29:16 (ASV)

The “inner part” here means not the holy of holies in particular, but the interior generally. The priests alone could enter the temple building. The Levites could penetrate no further than the inner court.