Hello everyone, I'm sorry for posting another double vanity question, but this forum truly is the best place to go for all things plumbing related and as I am not a plumber this was the best place to go. I have been able to find answers to all of my questions so far…which leads me to this one…which happens to be my first post. I think I have it figured out but I would like to make sure I am thinking about it correctly. I live in Georgia and our plumbing code our county uses is the International Plumbing Code. I am doing a guest bathroom remodel on a house built in 1970 which originally had one vanity initially installed in the guest bathroom, but it was also plumbed with the sink from the master (on the left side, other side of the wall). I want to convert this right side single sink set up to a dual vanity set up. The total number of fixtures on this 3 in vent line are at most three (there is on downstairs sink that may be vented) and once the new sink added would be four.

The way I see it there are three options,

Option 1: just hook up the drain from the new sink to the existing drain line. (I think this is incorrect b/c of siphoning issues with the other sink, but since this would be the easiest option I wanted to see if I was missing something.)

Option 2: Hook up the drain from the new sink to the existing drain line and then run a 1 ½ vent line straight up through the roof.

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Option 3: Hook up the drain from the new sink to the existing drain line and then connect into the stack (see picture).

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I think option 2 and/or 3 would meet code but I’m not sure, also any other ideas/options would be very helpful. Thanks again

Jason