פירוש על מקואות 6:8

העליון מן התחתון – as for example, that the upper [Mikveh] had drawn water and the bottom [Mikveh] had kosher/fit water.

Introduction Today's mishnah teaches how one can use one valid mikveh to make valid another mikveh valid.

והרחוק מן הקרוב – but we ae not concerned lest a person come and he stopped/interrupted the contact between liquids [so that the water of the ritual bath comes in contact with the impure water], and has immersion did not have any effect for him.

Mikvaot may be made clean [by joining drawn water from] a higher [mikveh to valid water] from a lower [mikveh or drawn water from] a distant [mikveh to valid water] in a [mikveh] near at hand. If there are two mikvaot on the sides of sloped ground, one can make the higher mikveh valid by having it touch (literally, kiss) the lower mikveh. If the two mikvaot are on equal ground, one can similarly make the one valid by having it touch the other mikveh. The mishnah will now demonstrate how.

מביא סילון של חרס או של אבר (brings a pipe of earthenware or lead) – and the same law applies of wood or of bone or of glass. אבר – lead.

How so? One brings a pipe of earthenware or of lead and puts his hand beneath it till it is filled with water; then he draws it along till [the two waters] touch even if it be by a hair's breadth it is sufficient. He takes some pipe made of either earthenware or lead and puts one end in the higher (invalid) mikveh. Then he closes up the other end of the pipe with his hand and draws it along until the water in the pipe touches the lower mikveh. Even if only a little bit of water touches the lower mikveh, the waters of the upper mikveh are validated.

ומניח ידו תחתיו – of the pipe in order that the water does not go outside when he fills it until the time when the waters come in contact and combine with the other [pure] Mikveh.

If in the higher [mikveh] there were forty seahs and nothing in the lower, one may draw water and carry it on the shoulder and place it in the higher [mikveh] till forty seahs have flowed down into the lower [mikveh]. In this case there are forty seahs of valid water in the upper mikveh but nothing in the lower mikveh. He can draw more water and carry it to fill up the upper mikveh because once it has forty valid seahs, no amount of drawn water renders it invalid. Then he can use a pipe to let water flow from the upper mikveh to the lower mikveh. In this way he can essentially use drawn water to fill the lower mikveh. Pretty neat!

אפילו כשערה – and they (i.e., the Rabbis) were lenient regarding drawn water which is Rabbinical. But if the upper [Mikveh] was lacking from its measure and he comes to make it fit through contact with the waters [of the lower Mikveh] to complete it to its appropriate measure, it is not enough with contact as much as a hair’s breadth, for even Rabbi Yehuda who is more lenient in the second chapter of [Tractate] Gittin [16a] as he requires moist enough to moisten other objects.

ממלא בכתף – that since after there are forty Seah of fit/kosher water in the Mikveh, even all of the drawn water in the world does not invalidate it.