Yoma 1:4-5

Yoma 1:4

The entire week leading up to Yom Kippur, the Kohein Gadol could eat and drink as much as he desired. The evening leading into Yom Kippur, they would not let him eat too much because that makes a person drowsy (and the Kohein Gadol was not permitted to sleep the night before Yom Kippur).

Yoma 1:5

The Sages from the Sanhedrin delivered the Kohein Gadol to the elders of the kohanim, who brought him to the upper chamber of the Avtinas family (who prepared the incense and would coach the Kohein Gadol). The elders charged the Kohein Gadol with the responsibility not to deviate from the prescribed order of the service (as the Sadducees would). He would turn aside and cry (for having been suspected of this) and they would turn aside and cry (because they likely accused an innocent person of potential wrongdoing).
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