Zevachim 22 - The Water Cistern (Kiyor)

The Kiyor was a large copper vessel, from which the Kohanim would wash their hands and feet. It had twelve spouts to avoid lines. The water in the Kiyor could come from any source, according to one opinion, but according to another, it had to come from a spring.

If the water in the Kiyor remained there overnight, it become invalid and had to be replaced. Therefore, they used to lower the Kiyor into a mikvah, with the help of a wheel, just before daybreak, and according to other opinions, at more time periods during the night.

Any Temple vessel could also be used for sanctifying the Kohen's hands and feet, but a regular non-sacrificial vessel could not. Why? Let's try to prove this by comparison with the copper base, in which the Kiyor stood. Since this base could not be used for washing the Kohen's hands and feet, even though it was a Temple vessel, isn't it true that a regular vessel surely could not be used? - No! The base is not made for storing water at all! Rather, this is derived from the word that the Torah used - "from it" - and not from other vessels!

Art: Jean-Baptiste-Simeon Chardin - The Copper Drinking Fountain