Answer :
Final answer:
Backwater valve is installed to protect fixtures from backflow of sewage.
Explanation:
Where a fixture is installed on a floor level below the elevation of the next upstream manhole, the fixtures shall be protected from backflow of sewage by installing a backwater valve. This valve prevents sewage from flowing back into the fixture during times of high water levels or flooding. It is designed to allow sewage to flow out of the fixture but not back in, ensuring the proper functioning of the sewage system.
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