Responsa for Eruvin 176:15
אמר ליה אביי והרי שופכין דאדם רוצה שיבלעו וקתני לא ישפוך
R'ELIEZER B. JACOB RULED: IF FOUR CUBITS OF A DRAIN WERE COVERED OVER'Our Mishnah<span class="x" onmousemove="('comment',' Which attributes to the Sages the view that water MAY BE POURED UPON THE ROOF.');"><sup>37</sup></span> cannot represent the opinion of Hananya,<span class="x" onmousemove="('comment',' Since he permitted this only in a courtyard but not on a roof The roofs spoken of were flat and had drains in the form of gutters into which rain water flowed and water was poured.');"><sup>38</sup></span> for it was taught: Hananya ruled: Even if [the area of] a roof was a hundred cubits no water may be poured upon it since a roof is not made to absorb water but to cause it to run down.
Teshuvot Maharam
A. He should fasten a board beneath the seat (within not more than three tefahim below the latrine walls) so that the feces first fall on the board and then into the ditch. Should the board break on the Sabbath, he would still be permitted to use the latrine on that day.
SOURCES: Cr. 178, 179; Pr. 96; L. 349; Mord. Shabb. 376; Hag. Mord. Shabb. 461; Tashbetz 38; Hag. Maim., Shabbat 15, 4; Kol Bo 31 (p. 34a). Cf. Terumat Hadeshen 66.