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Discussion Starter · #1 ·
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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Where I plumb a toilet requires a 2" vent. Tie it into your 4" vent stack 42" above finished floor. And yes you can use 3" for toilet drainage.
As far as the amount of turns in a vent, there is no limit as long as you install the vent graded uphill. The vent below the floor needs to have long sweep 90's and plumbed as a drainage line because its below the flood rim of the toilet.
 

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Okay, when you say plumbed as a drain line you mean to prime/glue all of the joints, correct?
Since the vent will be below the toilet, it needs to be treated as a drain line because it could possibly get water in it. Therefore drainage rules apply. use the proper fittings.
 

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Discussion Starter · #5 ·
Does this lav drainage/venting look better? I made the following changes:
- Changed location of 1st drain
- used 1-1/2" pipe for the drainage piping the wall (still used 2" going down to the basement
- re-studded the walls, put smaller holes in the studs
 

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