Im finishing out my attic as a bedroom and bathroom..I need to re-route a 3 inch cast iron main stack pipe from the downstairs bath( it goes straight up thru the roof in the middle the new attic bathroom under construction and I also need to run a separate 2 inch vent thru the roof for the new attic bath..a friend told me..I should put in something called ( studer vents ) ?...he says he has them in his restaurant...they dont have to go thru the roof..I've never heard of them..apparently it has a one way air valve or something..that prevents sewer gases from escaping...any opionions about this type of venting?..Thanks