Reference for Chullin 2:9
אֵין שׁוֹחֲטִין לֹא לְתוֹךְ יַמִּים, וְלֹא לְתוֹךְ נְהָרוֹת, וְלֹא לְתוֹךְ כֵּלִים. אֲבָל שׁוֹחֵט הוּא לְתוֹךְ עוּגָא שֶׁל מַיִם, וּבִסְפִינָה, עַל גַּבֵּי כֵלִים. אֵין שׁוֹחֲטִין לְגֻמָּא כָּל עִקָּר, אֲבָל עוֹשֶׂה גֻמָּא בְתוֹךְ בֵּיתוֹ בִּשְׁבִיל שֶׁיִּכָּנֵס הַדָּם לְתוֹכָהּ. וּבַשּׁוּק לֹא יַעֲשֶׂה כֵן, שֶׁלֹּא יְחַקֶּה אֶת הַמִּינִין:
It is not lawful to slaughter [so that the blood should run] into the sea, or in a river, or to place the animal within a vessel; but it is lawful to slaughter in a wet ditch, or within a utensil on board a ship. It is not permitted to slaughter in any pit at all, but it is lawful to make a pit within the house, that the blood may collect therein; but this is not permitted in the public street, not to countenance the custom of heretics.