Miszna do Liczb 19:9

Rabbi Yishmael says: there are three instances of lenient rulings by Beth Shammai and strict rulings by Beth Hillel.The book of Ecclesiastes does not defile the hands, according to the opinion of Beth Shammai; But Beth Hillel say: it defiles the hands. Water of purification which has done its duty: Beth Shammai pronounces it pure, But Beth Hillel pronounces it impure. Black cumin: Beth Shammai pronounces it not liable to become impure, But Beth Hillel pronounces it liable to become impure. So, too, with regard to tithes.

If [lying over the hatch] there were vessels made of dung, vessels of stone, or vessels of [unbaked] earth, everything [in the upper story] remains clean. If it was a vessel known to be clean for holy things or for [the water of] purification, everything remains clean, since everyone is trusted with [regard to matters of] purification. For clean vessels and earthenware vessels that are [known to be] clean protect with the walls of ‘tents'.

Bet Shammai say: hot water may not be immersed in cold, or cold in hot, foul in fresh or fresh in foul. But Bet Hillel say: it may be immersed. A vessel full of liquids which one immersed, it is as if it has not been immersed. If it was full of urine, this is reckoned as water. If it contained hatat waters, [it is unclean] unless the water [of the mikveh which enters the vessel] exceeds the hatat waters. Rabbi Yose says: even if a vessel with the capacity of a kor contains but a quarter-log, it is as if it had not been immersed.