99 Yoma 3/2-5

(2) And why did they need [to do] thus? For on one occasion the light of the moon appeared and they assumed that dawn had broken, and they slaughtered the tamid [daily offering], and they [had to] take it out to the place of burning [because the offering was not offered at the proper time]. They took the High Priest down to the place of immersion. This is the rule in the Temple: all who move their bowels require immersion, and all who urinate require washing of the hands and feet.

(3) No person comes into the Temple court for service, even if he is already ritually pure, until he immerses. Five immersions and a total of ten ablutions of hands and feet are performed by the High Priest on this Day. All this takes place in the courtyard above the Beit Parvah, except for this one [upon entering the Temple compound, which was performed near the High Priest's chamber by the south gate].

(4) They spread out a linen sheet between him and the people. He stripped off [his clothes], went down and immersed himself, came up and dried himself. They brought him the golden garments, he put them on and washed his hands and feet. They brought him the tamid [offering]. He cut its throat and another finished [the slaughtering] for him. He received the blood and sprinkled it. He went inside to offer the morning incense, to trim the lamp, and to offer the head, the limbs, the chavitim and the wine.

(5) The morning incense was offered between [offering] the blood and the limbs. The afternoon incense was offered between [offering] the limbs and the wine libations. If the high priest was elderly or squeamish, water would be heated for him and poured into the cold water [in which he would immerse] in order to take the cold edge from it.