I am replacing a double sink vanity with a new double sink vanity. For reasons i will not go into I can not alter the back of the vanity. The drain pipes (s) going into the sink drain , coming out of the wall need to be moved up about 3 inches (coming out of wall) to clear the back of the vanity.

I have opened up the drywall and I see that the pipes are horizontal and then do a curve to go through the wall. My question is can I cut the PVC pipes (on both sides) and install a S shaped connector to raise the pipes. I will do this on both sides since it is a double sided sink. The existing pipes are going through a stud lumber, so I do not want to disturb where they go through the stud.

What am I missing?

Normally , I would hire this out, but this is my personal residence & I don't want anyone in the house during Covid.

In my head I don't exactly see your situation, but that doesn't matter. I've had this same problem dozens of times replacing bathroom vanity cabinets with different drawer and door configurations. The rough plumbing has to be moved -- drain and sometimes a hot or cold supply valve.

The are plumbing codes that matter. A 1-1/2 inch drain line can only go a curtain distance to the air stack location. So if you are going to extend the drain line more than a few inches, you could be in for a world of hurt with drainage issues.

I will do a dry fit to ensure things line up before gluing the new drain pipes together.

AND you need to make sure you have access to run a snake to clear the line. Tenants and bathroom drain's always have lots of hair. Sometimes instead of just having the sink drain drop go into a trap then into the wall, you can install a "Y" fitting with a removeable cap, as a snaking port.

When i looking at youtubes about this they mentioned something about "vent ?", not going past vent (I didn't really understand it). Is that what you are talking about?

When i looking at youtubes about this they mentioned something about "vent ?", not going past vent (I didn't really understand it). Is that what you are talking about?

So I am now reading about AAV (Air Admittance Vents). I assume my next move is to open up more of the drywall so I can see where the AAV is located.

Oh good gosh. IGNORE THE VENT NONSENSE! All you're doing is moving an existing drain up 3". The horizontal drains are going into a main stack that goes down to the sewer, correct?

I'm assuming that this is an old double bowl sink one of the horizontal ones comes out of the main stack to the left and the other comes out of the main stack to the right, correct?

The vanity that you have had there for many years drained fine, correct??

If the answer is yes and your horizontal drains are on the left and the right of the stack going down to the sewer, you need 2 street 90's on each end.

Laura, I truly understand that some folks are vulnerable or extra cautious with Covid. However, a plumber in your bathroom and possibly your cellar is not giving you any germs. Don't climb under the vanity with him. Don't go in the bathroom with him. Don't hold the pipes while he glues them. Stay in another room, thank him when done and wipe down whatever you think he touched.

Laura someone has thrown a monkey wrench into your plan by mentioning the air vent. Its a sink drain for gosh sakes not a toilet flushing or washing machine drain.

I vote for NE ---- post--- why aren't you spackling?