פירוש על מקואות 2:8

הסייד – an artisan who plasters the pit/cistern with plaster/lime in order that it hold its waters, and his practice was to bring the lime/plaster in a common earthen vessel/pot , and that pit/cistern had kosher water in it but when the common earthen vessel/pot was sunk in the water and became filled up.

A plasterer forgot his lime-tub in a cistern and it became filled with water: if water flowed above it a little, it may be broken; and if not, it may not be broken, the words of Rabbi Eliezer. This is a similar situation to yesterday's mishnah. A plasterer, probably making the cistern, forgot his lime-tub in a cistern. Water then collected in the cistern, entered into the tub and then overflowed. The water in the tub now counts as if it was in the cistern. If he wants to make the cistern into a valid mikveh, he can break the tub and take it out. However, if the water has not overflowed the tub, then the water in it counts as drawn water. Therefore, he can't break the tub and let the water into the cistern.

אם היו המים צפים על גביו כל שהוא ישבר – so that the water not become drawn, for all the while that they are combined/mixed. But if he would raise the common earthen vessel/pot in his hand, they would stop and would become detached.

But Rabbi Joshua says: in either case it may be broken. Rabbi Joshua again rules leniently the water does not count as drawn water and does not disqualify the mikveh.

ואם לאו – that the waters did not float on top of it.

לא ישבר – and we are speaking of when it is not the rainy season. For if it was the rainy season, since there is water in the pit/cistern, he should break it.

רבי יהושע אומר בין כך ובין כך ישבר – for it is able to continue, as we explained above [in Mishnah 7].