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Eruvin 88

88b

The Mishnah and Gemara discuss the laws of an Ukah (pit) and a Biv (pipe) with regard to water disposal and describe how one may pour waste water into his Chatzer on Shabbos. How do these laws apply today with regard to pouring water on Shabbos into the drain of a sink, or using any other modern means of waste water disposal on Shabbos (such as flushing a toilet)?

The Mishnah differentiates between two different means of water disposal: (1) pouring water into one's Chatzer and letting it overflow into Reshus ha'Rabim (the Ukah), and (2) pouring it into a pipe (Biv) which brings the water directly to Reshus ha'Rabim.

(1) THE UKAH -- If the area of a Chatzer is 16 square Amos or larger, whether it is rectangular in shape (long and narrow) or square, it is permitted to pour out water into the Chatzer, because the Chatzer is large enough that the water will be absorbed into the ground before it flows out into Reshus ha'Rabim. If the Chatzer is smaller than 16 square Amos, and cannot absorb the full Se'asayim of water that a person tends to use every day, a pit must be dug to accomodate the remaining water.

This pit is only necessary in the summer season, when people prevent their Chatzeros from getting wet and muddy. Without a pit, a person does not want the water to stay in the Chatzer and make it muddy, and therefore he is pleased that it flows out into Reshus ha'Rabim, therefore it is prohibited to pour water in the Chatzer. In the winter, though, no matter how small the Chatzer is, one may pour as much water as he wants into it, even without a pit to receive it (like the ruling of Abaye). He does not care whether the water stays in the Chatzer or flows out, because the Chatzer is already muddy from the winter rains.

(2) THE BIV -- Rebbi Eliezer ben Yakov says that one may pour water directly into a Biv (pipe) as long as it is at least four Amos long. The Chachamim say that one may not pour water directly into a Biv because it will come out into Reshus ha'Rabim with such force that people will think he is standing right next to Reshus ha'Rabim and pouring it directly into Reshus ha'Rabim (which, of course, is forbidden). Rather, the Chachamim maintain that one may pour the water only near the Biv but not into it.

However, Rashi (88a DH Lo Yishpoch) writes that the Biv, too, must be broad enough to absorb Se'asayim of water (i.e., 4 x 4 Amos, and not just 4 Amosh long.)

HALACHAH: The RAMBAM rules stringently, in accordance with the Chachamim, that one may pour water near the Biv but not into it. Others, though, rule leniently, and the MISHNAH BERURAH (OC 357:21) is lenient as well and permits pouring water directly into the Biv.
However, the SHULCHAN ARUCH (OC 357:2) rules, based on Rashi, that one may only pour water into a pipe that goes into Reshus ha'Rabim only if the pipe is made of an absorbent material. If so, one should not pour water into metal or plastic pipes (such as the ones used in modern residential drainage systems), whether one pours it directly into the pipe or only near the pipe, if the pipe leads out into Reshus ha'Rabim. However, in OC 357:3, the Shulchan Aruch writes that it is only forbidden if the outlet of the water opens to an actual Reshus ha'Rabim or a large public street (Karmelis) in the city. If it opens into a valley, sea, or any other Karmelis *outside* the city, it is permitted to pour water into that pipe. Since modern sewage systems lead to a Karmelis outside of the city, it is permitted to pour water down the drain, even directly, on Shabbos.