Where should the vent be coming off of a bathroom sink?

[Fee]

I am connecting a basement sink vent to an existing bathroom sink above it. Currently the existing bathroom has the trap arm dropping to the drain and then about 2ft below the sink it tees off to connect to the yellow vent. This seems incorrect. Am I able to connect the new vent into this setup or should I move the vent to come off of the trap arm like in picture two?

New setup

 

[AC Power]

Picture #2. It's called wet venting. This is assuming the yellow pipe going up ↑ (in your drawing) is the main stack. This yellow main stack goes to the rooftop.

 

[Fee]

Here is an updated pic. So the trap would tee into a wet vent, with the blue drain going down to the basement and the yellow vent going vertical and exiting through the roof. Meanwhile the basement sink vent would run up and tie into the vent at least 6" above the sink. Does this seem correct?

 

[AC Power]

That would work, yes. One purpose of venting it this way is to prevent the drain water from the upstairs sink rushing past tee of the downstairs sink siphoning the trap empty (AKA: venturi effect).

 

[Fee]

Thank you for the response. Just for my knowledge, is the current upstairs vented correctly with having the tee coming off of the drain at the floor level vs up higher?

 

[AC Power]

Being there is nothing draining into the pipe ABOVE the tee, it is fine, yes.