Zevachim 22A

בין שאין בהן רביעית; ובלבד שיהו כלי שרת!

or they cannot hold 1/4th-log of water, provided that they are service vessels. Apparently, the Basin need not hold so much water.

אמר רב אדא בר אחא: בקודח בתוכו.

Rav Adda bar Aḥa says: The baraita is referring to a case where one drills a hole in the Basin and places a much smaller vessel at the hole as a conduit for the water. Even if that vessel is very small, the priest may sanctify his hands and feet from it, provided that there is enough water in the Basin for 4 priests.

והא ״ממנו״ אמר רחמנא! ״ירחצו״⁠ – לרבות כלי שרת.

The Talmud asks: But doesn’t God state that the priests must wash their hands and feet “from it,” i.e., from the Basin and not from another vessel? The Talmud responds: The following verse repeats the phrase “they should wash,” to include any service vessel.

אי הכי, כלי חול נמי! אמר אביי: כלי חול לא מצית אמרת, מקל וחומר מכנו; ומה כנו, שנמשח עמו ⁠– אינו מקדש; כלי חול, שאינו נמשח עמו ⁠– אינו דין שאינו מקדש?!

The Talmud challenges: If so, then it should be permitted for a priest to use a non-sacred vessel as well. Abaye says: You cannot say that a priest may sanctify his hands and feet from a non-sacred vessel, since the matter may be derived by a fortiori inference from the halakha concerning the base of the Basin: And just as its base, which was anointed along with it (see Exodus 40:11), is still not fit for a priest to sanctify his hands and feet with water from it, then with regard to a non-sacred vessel, which was not anointed along with the Basin, is it not right that it is not fit for a priest to sanctify his hands and feet with water from it?