I am adding a large bathroom in an attic with double lavs, a shower and toilet. Based on my floorplan, I am venting everything individually because I do not want to drill through the floor joists. Since my lavs and shower will have a plumbing wall, I am going straight through the roof for venting, which is intuitive and easy. However, my toilet is on the other side of the room and I would like to tap into to my original 4" dry vent for my first floor fixtures, in order to vent the toilet. I have attached the picture. I need to get the low-heel 1-1/2" connection tapped into my 4" vent. Are there any restrictions or general rules that dictate how I do this? For instance, can I only tap into the 4" at a certain height? Or can I only have a limited number of turns? Ideally, I would like to run the 1-1/2" in the sub-floor (with a slight upward slope) around the 4" drain and then connect on the backside (rightside in the photo). I want to build a short wall for astetics on the left side of the 4" dry vent. Also, can I use a 3" street 90 degree bend as my toilet connection? Or do I have to use a 4" to 3" closet bend? (In the picture I have a 3" street 90.
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