Welcome to the wonderful world of plastic the noisy piping systems and improper venting
Even Charlotte piping corporation the manufacturer of plastic and cast iron say for quiet trouble free systems use cast iron and to be cheap use plastic on venting
Replacing the steel pipe which you thought was "Black" was either no hub cast iron or painted galvanized steel piping.. "black steel" is used on either steam, hydronics, or gas piping never on drainage as the oxygen in the water would corrode it out with in a very short time.
Installing a vent indoors is always a great idea if a person is looking to sell the house and has total disregard to possible sewer fumes entering the structure.
Only someone who has total disregard for quality of life issues would allow a device to possibly fail, relying on a piece of rubber to protect the inhabitants from sewer fumes which contains methane, carbon dioxide, sulfur dioxide, and nitrous oxides. In addition, chlorine bleaches, industrial solvents, and gasoline are frequently present in municipal and privately owned-sewage treatment systems.
Sewer gas is a complex mixture of toxic and non-toxic gases that can be present at varying levels depending upon the source.
It is formed during the decay of household and industrial waste. Highly toxic components of sewer gas include hydrogen sulfide and ammonia.
Sewer gas also contains methane, carbon dioxide, sulfur dioxide, and nitrous oxides. In addition, chlorine bleaches
The principal risks and effects associated with exposure are:
Hydrogen sulfide poisoning. Exposure to low levels of hydrogen sulfide causes irritation of the eyes and respiratory tract. Other symptoms include nervousness, dizziness, nausea, headache, and drowsiness.
This gas smells like rotten eggs, even at extremely low concentrations. Exposure to high concentrations can interfere with the sense of smell, making this warning signal unreliable. At extremely high levels, hydrogen sulfide can cause immediate loss of consciousness and death.
Asphyxiation. Methane acts like carbon monoxide, blocking oxygen in the blood, and can similarly cause suffocation and death at high levels. Exposure to lower levels can produce flu-like symptoms such as headache, nausea, and drowsiness. Breathing undiluted sewer gas, even for short periods, as in a municipal sewer line or a manure storage tank, can result in suffocation and death. Sewer gas diffuses and mixes into indoor air, and will be most concentrated where it is entering. It can accumulate in basements.
Explosion and fire. Methane and hydrogen sulfide are flammable and highly explosive.
YUP using a vent INDOORS rather then spend the money to hire a professional licensed master plumber who knows how to vent fixtures properly is the way to go IF you plan on selling the home and have total disregard to quality of life issues.
This is your home and it is an investment VENT all fixtures to the out doors and have the venting connect to a vent terminal on the roof.
There are some folks who just don't know or have been poorly trained and dabble in plumbing who never bothered to attend a five year apprenticeship training program and thus think AAV's are the way to save money and do not take the ramifications of product failures into account
By the way you do know that your new tub with 2 ft of water in it will weigh in @ 2,250 pounds not including people or the weight of the tub itself and of course you took this load factor into consideration prior to the installation?
Good luck Sylvan Tieger,LMP