Lowering a Kitchen Sink Drain Line

Hello,

I just installed a 10" undermount sink- used to have a 8" above. Nice surprise when I figured out the drain line was too high.

I am planning on cutting open the wall to lower the drain in the main line.

Couple questions:
Currently the main drain travels 24" horizontally connected with a Tee at the 2" main line. That 2" pipe is vented to the roof. Is that vented correctly?

Can I just open that line and do the same thing lowering it to the appropriate height? Is the Tee creating a vent? Can I use a Fernco Quick Tee to make the new connection? The line is galvanized pipe.

Do I need to slop the horizontal line downward toward the main line?

I attached a photo when the wall was open. Of course now it is all drywalled and has a nice cabinet in front.

Thanks!

 

Cut the T out with enough pipe beneath and above to allow for a stub to be glued into a pvc (or abs, whatever is generally used in your area) to a sanitary T (I can never remember if that must be a sanitary T or a wye - since above is a vent, I think a sanitary T is okay), not a t like is there now, and a stub above then use nohub connectors to reattach that new assembly that you cut out. The pipe coming up from below is likely a revent from something below (maybe the laundry or a sink in the basement?). Note that, depending on what's above, once you cut the pipe, it might move. To ensure that doesn't happen, you might want to install a hanger brace.