Which of the following is a one-way check valve that allows air to flow into the piping system without letting any of the sewer gasses leave the DWV system?

Question

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An Air Admittance Valve (AAV) is designed to allow air to enter the plumbing drainage system when negative pressures develop in the piping system. This prevents sewer gases from escaping into the building by only opening under negative pressure to let air in, which helps to balance the pressure within the drainage system and prevent the trap seals from being siphoned off.

Which of the Following Is a One-Way Check Valve That