Mishnah 15 - Chapter 5 - Pirkei Avot

There are four middoth (levels) in those who sit before the sages: [(Above, [Mishnah 12], the subject is remembering and forgetting; here it is logical reasoning and discriminating what is right from what is not right]: a sponge. [Just as a sponge absorbs muddy water together with clear water, so there is a disciple whose heart is "broad" and accepts whatever he hears, lacking the power to discriminate between the true and the false], a funnel, a strainer, and a sieve. A sponge — it absorbs everything; a funnel — it takes in at one end and releases at the other. [So, there is a disciple who emits whatever he absorbs]; a strainer — it releases the wine and retains the lees. [So, there is a disciple who releases whatever he has learned in the house of study and retains only idle talk]; and a sieve — it releases the flour and retains the meal. [After the bran and the bruised grain are extracted from the ground flour, and there remain the thin flour with the thick meal, the desired part, it is put through a very thin sieve, so that there descends all that thin flour, like a white powder, and there remains only the thick, desirable, meal. (This is how meal-offerings were prepared.) Similarly, there is a disciple who has the ability to sift what he has heard and to discriminate the truth from the false and the vain.]