I'm planning to move the kitchen in an apartment, and need to tap a drain line into existing plumbing of 4" cast iron and 2" galvanized. Any critique or better plan would be appreciated. I don't trust the local plumbers to plan this stuff well, the last job it took 3 plumbers to finally get it right.

Since I don't want to mess with the ancient cast iron I want to cut into the 2" to mount PVC T's with rubber couplers. This apartment is identical to the ones above and below on the same vent & soil stacks. I'm not certain why there's a parallel vent coming from the unit below, there isn't a corresponding one from this unit to the one above, which is the top floor. The run of 2" to the new kitchen sink is less than 7' so I should be okay with the local National Standard code. I know the vent tie in needs to be 24" above the basin top.

Here's a drawing of the existing plumbing, with the proposed addition in red. Any thoughts would be appreciated.

{{!gwi}}