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4 in Corrugated Drain Backflow Flap Insert
A print-in-place check flap that pushes into the open end of 4 in (100 mm nominal) corrugated French-drain or sump discharge pipe. Eighteen 1.4 mm flex fins (106 mm across) fold down to grip the pipe wall. Outflow swings the 74 mm hinged flap open on its 4 mm printed pin. Backflow, critters and leaves press the flap shut against a 45° conical seat. It is a light-duty seal for gravity drains, not a pressure-rated valve, and is 9 mm thick. Print in PETG or ASA if it will sit in the sun.
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