Related for Pesachim 83:6
מי תשמישו של נחתום וכו': תני חדא שופכין במקום מדרון ואין שופכין במקום האישבורן ותניא אידך שופכין במקום האישבורן
The School of Rab interpreted: Lemor, a negative injunction [law] was stated. THE WATER USED BY A BAKER etc. One [Baraitha] taught: You must pour [it] out on a slope.
Tosefta Pesachim
Water that was used by bakers may be poured out in a level place, but it may not be poured out in a place with a downward slope (קטפרוס) because it gathers together and becomes leavened.
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