Nice site here...Solid answers...

I'm installing a wet bar to a finished basement...And a shower bathroom to existing rough-in plumbing...The bathroom is all vented to what appears to be a secondary vent that is a 2" pipe...

The wet bar will be around the corner and will be approximately a 10' run if I tap into the bathroom rough-in...

Directly behind the wet bar is a 3" stack that has a 1st floor toilet attached...And a cleanout...I believe it is not to code to tap into any stack that has a toilet upstream...Is this correct???

Can I install the 1 1/2" wet bar drain underground and 90 up into the wall cavity, keeping it lower than the wet bar trap??? And can I tap into that 3" stack with the 1st floor toilet attached???

If I take it around the corner to the bathroom rough-in it will be a 10' run...Is that too long???

Basically I want to know if I can tap that 3" stack with a 1st floor toilet attached...And if it meets code to run basement plumbing underground and 90 up into a wall cavity as long as I stay below the trap level of the wet bar...Or should it be run underground the entire way to that bathroom rough-in and tapped in underground...

speedball1

I would keep the underground drainage at 2". . You may connect to that stack only if you vent the bar sink.
I would use a short sweep to get around the corner. Since the bar sink vent will come off the top of the san tee and revent back to a dry vent a 10' run is acceptable.
You are proposing to install a "dog leg" in the bar sink drain line. I would keep the drainage underground and hold the 90's to a minimum. Good luck, Tom