How to change elevation in long kitchen sink drain line

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Dbolljr9

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Background: The kitchen sink in my house is located far away from the rest of the plumbing fixtures. It has its own 2" stack and a long horizontal cast iron drain line that runs under my basement floor to join up with main line out of the house. Recently, this 2" line has clogged under the basement floor and I am planning on routing a new PVC drain line overhead in the basement to the 4" cast iron stack at my hall bath, and abandoning the underground cast iron drain. I have attached a sketch of the plan.

I have two questions.
1. Most of the run is horizontal (1/4" per foot) but I need to drop about 12-24" near the 4" stack because the 4" drain from the hall bath toilet to the stack is in the way. Is it better to change this last bit of elevation with 45° incline (dashed line) or with a vertical drop/90° elbows (solid line)?
 

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Dbolljr9

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It appears my second question didn't post.

2. I will be cutting the cast iron stack to insert a new sanitary tee with "shielded" no-hub couplings. Should this new 4x2 tee be cast iron or PVC? I will be adding support to the cast iron piping above, but I am still a little concerned about the weight of the cast iron on top of the PVC fitting.
 

John Gayewski

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It appears my second question didn't post.

2. I will be cutting the cast iron stack to insert a new sanitary tee with "shielded" no-hub couplings. Should this new 4x2 tee be cast iron or PVC? I will be adding support to the cast iron piping above, but I am still a little concerned about the weight of the cast iron on top of the PVC fitting.
Pipe that spans from floor to ceiling should be supported from above and at the floor. Using a pvc tee would be my choice with a riser clamp at the floor.

Wye into the stack. Long sweep 90 or combo with cleanout horizontally.
 

John Gayewski

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Thank you for commenting.

To clarify - you think I should use a wye instead of a sanitary tee at the sewer stack, and that the 2" pipe should approach the wye at a ~45° incline (like the dashed line in the sketch)?
Yep
 
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