Adding a sink on the 2nd floor

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|________________ ->2nd floor
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|__________
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|__________|______ -> 1st Floor



In my little diagram there are 2 sinkse on the basement level. Both this sinks have 2" drain lines up to the T's as they both wet vent toilets.
Now the vent that goes upstairs and terminates is on the 2nd floor through the roof. Now the owner wants to put a kitchenet on the 2nd floor off of the office. How can I tie it in without breaking code? The vent is only 1.5". Would I have to make the 2nd sink have an individual vent that goes up and ties in above the flood rim of the purposed kitchen sink? OR can I just Tee into the vent line and everything will be fine?

No ........................

yeah I was pretty certain that if the KS drained into sink #1 and sink #2 had an indivual and continous vent it would be okay. Or if I had to leav the vent the same I could drain the KS into the 2" below the sink #1 with a 2" wye and 45.

Any plumbing upstairs will have to tie in "below" the downstairs plumbing.
You can't "dump" a sink down a vent can call it plumbing.
Have you ever seen how sharp a bend a vent 90 is? And santees turned upside down? No.
And what happens when you pull the plug and let the kitchen sink drain down?
It siphons out all the traps below it.

You would have better look dumping a bucket out the window. At least it wouldn't' mess up the plumbing below.

You DO NOT have to vent the new sink, but you DO have to restore the vents for the lower fixtures since you are changing their vent pipe to a drain pipe, and you cannot "wet vent" between floors.