Zevachim Daf 21 זבחים דַף 21

The Gemara asks: מהו לקדש ידיו [ורגליו] בכיור – what is the halachah whether a Kohen can sanctify his hands and feet by immersing them in the kiyor? Since the passuk says to wash "ממנו" – from it, does that imply ולא בתוכו – but not inside it, or does it even allow for immersion in the כיור? A proof is suggested from a Baraisa teaching that a Kohen who immersed himself in מי מערה – water in a pit (i.e., a מקוה) and performed avodah, it is invalid. This implies that if he would similarly immerse (his hands and feet) in the כיור itself, it would be valid!? The Gemara rejects this inference, because the Tanna needed to teach that טבילה in a מקוה is not valid, so one should not reason: כל גופו טובל בהן – he can immerse his entire body in [a mikveh] and become tahor, ידיו ורגליו לא כל שכן – is it not certain that it should be effective for his hands and feet? [The כיור’s water, which is שאובין – drawn, is not valid for טבילה.]

Rebbe Chiya bar Yosef said about the כיור’s waters: נפסלין למתירין כמתירין – they become disqualified for the “permitters” like the permitters do, לאברים כאברים – and for the limbs like the limbs do. Meaning, just as the "מתירין" of korbanos (e.g., the blood which permits their consumption), become disqualified at sundown, so too מי כיור which were not submerged in the בור at sundown (or any time during the night) are disqualified from being מקדש ידים ורגלים for avodah with מתירין. And, just as אברים become disqualified by daybreak, one cannot be מקדש for avodah with אברים from מי כיור which were not submerged at daybreak. Rav Chisda holds that מי כיור are only disqualified at daybreak, even for מתירין. Rebbe Yochanan ruled that once the כיור is submerged (before שקיעה), it is not raised again until daybreak. Although he holds (like Rav Chisda) that it may be used at night for avodah with אברים, he holds of גזירת שיקוע – a decree requiring the כיור’s submersion the entire night, to ensure it would be submerged at daybreak, when he holds the unsubmerged מי כיור would be disqualified. If the כיור is raised to be מקדש for תרומת הדשן, it is immediately resubmerged before daybreak.

Rebbe Yose bar Rebbe Chanina said: כל כיור שאין בו כדי לקדש ארבעה כהנים ממנו – a kiyor which does not have sufficient water to be מקדש four Kohanim’s hands and feet from it, אין מקדשין בו – [Kohanim] cannot sanctify themselves with it at all, because the passuk says: ורחצו ממנו משה ואהרן ובניו – “Moshe, Aharon, and his sons will wash [their hands and feet from it]” (totaling four people). This is challenged from a Baraisa, which states that all כלים sanctify their water for קידוש ידים ורגלים, whether they contain a רביעית of liquid or not, provided they are כלי שרת!? The Gemara answers: בקודח בתוכו – the case is where one bores through the side of the כיור, and this כלי fills the hole, allowing water to flow from the כיור, which does contain enough water for four Kohanim, outwards through the כלי.