Yet another double vanity sink question

[Average_joe]

I have a 60 eras ranch house in Des Moines IA on a septic system with one bathroom. The drain for the vanity runs horizontal to the stack. About 6' feet (1-1/4" copper) it currently is the highest connection on the stack. There is no separate vent. I would like to add a double sink. I'm wanting to know if I could Use a setup like this crudely drawn one in the pic however my horizontal pipe would be connected to the vent/drain stack?

Thanks in advance.

 

[Reach4]

Not permitted if UPC is in effect as it is in most of Iowa. However you could use an AAV. It needs to be able to draw air and to be replaceable.

 

[Sponsor]

 

[Terry]

You should bring 2" up to the double fixture cross, and then use an AAV for the vent.

 

[Average_joe]

You should bring 2" up to the double fixture cross, and then use an AAV for the vent.

Thank you guys for your quick response I know this stuff is your livelihood albeit not is this area but your help is greatly appreciated.
Should I plug or cap the existing drain line coming over from the existing stack?

 

[Terry]

You can cap the old line.