Here is an explanation of the valve!
An air admittance valve (AAV, sometimes known as "cheater vent") allows air to enter the plumbing drainage system through a one-way air valve when a plumbing fixture is operated. When the flow stops, the valve closes by gravity or a spring and prevents the escape of sewer gas from the plumbing system. AAVs allow greater freedom of design for engineers and architects; the classical application is for an island sink in a kitchen where running a vent upward is not possible. While some locations still prohibit AAVs, many codes now allow them. They do require inspection and infrequent maintenance, so they need to be installed in readily-accessible locations. Even where used extensively, at least one plumbing vent to the outdoors will still be necessary, but AAV-use can reduce the number of roof penetrations.
Here is another option if you're feeling froggy!
http://i115.photobucket.com/albums/n...mp/kitvent.jpg
Sink smarts. Although island plumbing eventually connects to a vent stack that penetrates the roof, most building codes require a high venting loop within the base cabinet. This drawing is based on requirements in the National Plumbing Codes Handbook.
Use 1 1/2-in. PVC pipe in the vent loop as well as to the main drain line.
Plan drawers and cabinet space around the plumbing, and make sure there's room to get at the pipes for repairs.