Answer :
Final answer:
Air-admittance valves are used to protect traps from siphonage by allowing air to enter the plumbing system during negative pressure events. Cisterns are not specifically designed for this purpose, while return and waste valves serve different functions. Maintaining the water seal in traps is crucial to preventing sewer gas escape.
Explanation:
Protection Against Siphonage in Traps
Siphonage is a condition that occurs when the water seal in a trap is lost, often due to negative pressure in the drainage system. To protect traps from siphonage, one effective method is the use of air-admittance valves. These valves allow air to enter the plumbing system when a negative pressure occurs, helping to maintain the necessary water level in the trap and prevent the escape of sewer gas.
Other methods that could be mentioned are cisterns, which are tanks that can store water and might contribute to maintaining water levels, but they are not specifically designed for protecting traps. Return valves and waste valves are used in other plumbing applications to control water flow and prevent backflow, but they do not directly address siphonage issues.
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