I have a 1925 house with a 4" DWV line for the toilet. I want to wet vent my shower using 2"DWV ABS which is 2 feet from the 4" toilet waste line. Both the shower and toilet lines will be horizontal and about 6 feet from the soil stack.Is this possible with out a vent? this bathroom is in the middle of the house and a external vent not practical I also have minimum space for a AAV and would have to go up into the wall cavity to get 6" above the flood plane of the fixtures.