“The priests went into the inner part of the house of the Yahweh to cleanse it. They brought out all the unclean things that they found in the temple of Yahweh into the court of the house of Yahweh. The Levites took them. They carried it out to the Wadi Kidron. They began to sanctify on the first day of the first month. On the eighth day of the month they came to the vestibule of Yahweh. Then for eight days they sanctified the house of Yahweh. On the sixteenth day of the first month they finished.”
Only the priests could enter the inner part of the Temple. The Levites carried out all the filth from the courtyard of the Temple to the Wadi Kidron. All priestly purifications took 7 days, as outlined in Leviticus, chapter 14. Thus it took over 2 weeks to clean up the house of Yahweh. It is surprising that no one noticed the deterioration of the Temple since the Levites were there, even if the kings were indifferent.