pressure reduction device such as the PAPA positive air pressure attenuator to provide a complete venting solution for more complicated drainage venting systems. Using AAVs can significantly reduce the amount of venting materials needed in a plumbing system, increase plumbing labor efficiency, allow greater flexibility in the layout of plumbing fixtures, and reduce long-term roof maintenance problems associated with conventional vent stack roofing penetrations. While some state and local building departments prohibit AAVs, the International Residential and International Plumbing Codes allow it to be used in place of a vent through the roof. AAVs are certified to reliably open and close a minimum of 500,000 times, (approximately 30 years of use) with no release of sewer gas; some manufacturers claim their units are tested for up to 1.5 million cycles, or at least 80 years of use. AAVs have been effectively used in Europe for more than two decades. Island fixture vent An island fixture vent, sometimes colloquially called a "Chicago Loop", "Boston loop" or "Bow Vent", is an alternate way of venting the trap installed on an under counter island sink or other similar applications where a conventional vertical vent stack or air admittance valve is not feasible or allowed. As with all drains, ventilation must be provided to allow the flowing waste water to displace the sewer gas in the drain, and then to allow air (or some other fluid) to fill the vacuum which would otherwise form as the water flows down the pipe. An island fixture vent provides an elegant solution for this necessity: when the drain is opened, water displaces the sewer gas up to the sanitary tee, the water flows downward while sewer gas is displaced upward and toward the vent. The vent can also provide air to fill any vacuum created. The key to a functional island fixture vent is that the top elbow must be at least as high as the "flood level" (the peak possible drain water level in the sink). This is to ensure that the vent does not become a de facto drain should the actual drain get clogged. Cost The cost of installation is high because of the number of elbows and small pieces of pipe required. The largest cost outlay with modern plastic drain pipes is labor. Use of street elbows is helpful. Alternately if moving sink to an island sink, install the P-trap below the floor