To properly have ventalation through out the home and meet code you must have at least 1 vent running to the outside, this should be located at the highest branch as possible and be not less than 1/2 the diameter of the building drain (2" will do fine) From there you can now install AAV's, just remember that every trap and trapped fixture needs a vent. This includes washer machine, kitchen sink, bathroom sink, shower, tub, toilet. The best thing to do for the sinks is to visit a plumbing supply house (As lowe's or HD may not know or have what you need) and ask them for a AAV that you can retrofit to your s- trap or p-trap. It is a conversion kit (We have them here in VA at VAMAC Plumbing Supply) As far as tubs and showers go if you can get under the house you can install them right under the tub, toilet, shower by cutting out a section of pipe, installing a sanitary tee and install the AAV on top of that. Remember to install the AAV just below (Downhill) of the fixture. Also remember that you can not block in an AAV as they need unobstructed air flow. I would recomend using a quality vent such as Durgold as the cheaper kind they use in mobile homes do not meet code and they do not always seal out fumes. These depending on your area are about 20.00 a peice, but well worth it.