Toharot, Chapter Six, Mishnah Six
Today’s mishnah brings up some interesting cases in which a person can become pure and be made impure at virtually the same time.
1) If there was a broken [earthenware] vessel in the mikveh and utensils were immersed in it, they become clean from their [former] uncleanness but are again rendered unclean because of the earthenware vessel.
a) But if water flowed above it in any quantity, they are clean.
2) If [water of] a spring flowed forth from an oven and a man went down and immersed himself in it, he is clean but his hands become unclean.
a) But if [the water was as] high above the oven as the height of his hands, his hands also are clean.
Section one: An impure broken earthenware vessel is floating on top of a mikveh or the sea. Water is entering it from its sides. If one immerses vessels in this broken vessel they are clean. This means that the water in the vessel does not count as “drawn water” because the vessel is broken. However, there is a problem (isn’t there always?). An earthenware vessel cannot become pure by virtue of immersing it in a mikveh. [Earthenware vessels must be broken to become pure]. Therefore, this broken vessel is still impure. When one pulls out the vessel he is immersing, the water that comes up with it will immediately become impure by being in the airspace of the impure earthenware vessel. That water will then defile the vessel being immersed, as liquids always do.
However, if the earthenware vessel is fully immersed in the water of the mikveh, then the water above it is pure because it is part of the mikveh. Thus if he immerses the vessel on top of the earthenware vessel, when he takes it out, it will be pure.
Section two: An impure earthenware oven is set or even attached to the ground, as was the custom with ovens. Suddenly, a spring bursts forth from the ground through the oven (thereby ruining the pot roast, but that’s another issue.) One can immerse in the spring inside the oven. However, his hands which will be inside the oven’s airspace when he comes out, will be defiled.
But if the water flows over the oven by at least the height of his hands, then when he comes out, his hands will be immersed in this water. If this is the case, they will remain pure.