Sforno on Exodus 30:18/ספורנו על שמות ל׳:י״ח

1ועשית כיור, this is another vessel which has not been mentioned before with the other vessels that were part of the Tabernacle. The reason is that the basin was not instrumental in attracting the presence of the Shechinah to the Tabernacle. Its function was merely preparatory to the priests’ service in the Tabernacle.