Going from single to double sink

I am going to go to a double sink. The pipe is iron pipe, 1 1/2". There are no unions in it anywhere so i will have to cut it at the top red line. and just below the wye. I want to use a pvc double wye using no hub couplings. Will this work and is it the proper way to do it? Thanks

 

You need this. Only one connection to the nipple coming out of the wall:

SnappyTrap 1-1/2 in. All-in-One Drain Kit for Double Bowl Kitchen Sinks-DK-110 - The Home Depot

 

I should have mentioned, this is for a bathroom vanity.

 

Yes, I think adding a double wye will do what you need. You'll want to be sure to anchor the upper section of galvanized pipe before cutting it. It will probably drop if you don't - which may cause damage to both your fingers and the seal at the roof.

BUT... there are some details regarding a double wye which I'll defer to Lawrosa (Mike) here who is the expert on the code-specific details.

 

Double wyes in this application aren't up to code therefore I would use a double sanitary T.

 

What is the difference between a double wye and a double sanitary? It looks to me like the double wye would drain better. not arguing, just curious. Thanks for the replies.

 

It's a venting technicality. On a wye in the vertical, the point where the "vent" starts is below the actual drain or trap arm. On a T, which has a much shorter sweep, the point the vent starts is just above the drain. Where the top of the horizontal drain pipe hits the sanitary T is considered the start of the vent. Would it ever make a bit if difference how the fixture drains? I really doubt it. I think they look at it from a standpoint that because it's a dry vent if the system ever backs up, it would start backing up into the vent pipe before the drain.
They have diagrams that explain this too. Lawrosa might be better at that.

 

I think the sanitary T will be easier anyway as the pipe will run straight across instead of at an angle.

 

Thanks for the clarification SD Plumber. I knew there were rules with double fixtures, but can never seem to get my head around the specific requirement.