RectorSeal has introduced the Magic VentT Air Admittance Valve that protects the trap seal from siphonage without the need for additional piping to the outdoors. When used in combination with the Magic TrapT fitting, Magic Vent is quick and easy to install in under-sink applications, eliminating unsightly roof penetrations. Whenever the drainage system is subjected to a negative (reduced) pressure, Magic Vent opens to admit air, which balances the pressure in the drainage system, protecting the trap seal. Upon reaching a neutral pressure, Magic Vent closes by gravity to form a tight seal, thus preventing any transmission of sewer gases through the valve. RectorSeal.