I have a 1.5" galvanized nipple coming out of wall. Is it best to use a shielded coupling or a pvc female adapter to connect the trap. Or neither? Should I connect the wall bend directly to the nipple?

Also should I wait to screw the new vanity into the wall and connect the trap first?

One problem I see, if I center the vanity correctly in line with the medicine cabinet above.... the nipple coming out of the wall will not be centered on the inside of the cabinet nor will it be centered with the drain hole of the sink.

Should I center the vanity with the drain or the medicine cabinet?

how you attach to the galvanized nipple depends on the condition of the threads.
I would use a shielded no-hub coupling before I would use a female adapter.
another option is to use a brass slip nut with a plastic washer to adapt to a tubular trap ( providing the threads are good)
center the vanity on the medicine cabinet..

"center the vanity on the medicine cabinet.."

So its not necessary that the stubout and the sink drain are centered? How do I make up for that difference? The j-bend rotates toward center?

yeah, the j-bend will rotate towards the center and will make about 2-3 inches in offset.
more than that and you gotta use a 45 or 22..

If I use a shielded coupling... what size do I need to accommodate the nipple and the piece of pvc.... is the nipple and a pvc the same 1.5"?

yup, the outside diameter is the same. make sure to clean out the galvanized pipe as they tend to collect hair etc..

I would remove the nipple before the cabinet is in place while there is room to work and a much better angle for leverage to unscrew it. Then you can do what you need to do to make things line up with all new parts and more options.

Not a plumber

I previously suggested using a rubber coupling connection on a wall connection to a poster who was having problems with a wall drain connection. I also said I did not know if it was code correct but that I thought it should be.

I was then advised to not try to decide what should be code or not, but just to do whatever you (I) do every day. (IE - Guess I should stay with my day job.)

My reasoning is a small/slow leak at a wall connection may go undetected draining down within the wall possibly causing extensive water damage. Proper and secure threaded / slip connections at the wall may be a little "iffy" in the long run - by a DIYS'er. Installing a shielded rubber coupling at a wall connection is easily done by a DIYS'er and "should be" leak proof. Leaks that may happen under a sink in the open are more likely to be seen and corrected. Personally I use a rubber coupling with mostly glued PVC and only the minimum slip connections.

Thanks so much everyone. I used a shielded coupling and it was very easy. Also everything lined up perfectly.

The only thing I question is the tailpiece that came with the faucet.

I did not cut it. It extends 3 or 4" into the slip hub and pvc that goes before the jbend.

Should I have cut it or is it ok to extend into the pipe as I describe?

Leak testing everything now.... crossing my fingers.

you don't want the tailpiece to contact the bottom of the j-bend.
that would restrict the flow. otherwise, no problem...

Thank Packy... last question....

This was a small bathroom vanity sink.

I used a 1.5" P-Trap (regular pvc fittings not the flimsy stuff in the kits).... everything seems to fit excellent... however, is that too big of trap for a bathroom sink?

A friend told me it should have been 1.25?

you are good to go

you used a 1.5 X 1.25 slip joint washer to attach the 1.25 tailpiece

(the trap nut also was 1.5 X 1.25 hole)

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

"(the trap nut also was 1.5 X 1.25 hole)"

Actually the trap has a union. I could have picked three kinds of PVC traps... one with the union, another without a union and another that had a small cleanout in the bottom.

The only 1.5x1.25 connection is where the tailpiece connects with a trap adapter (glued one side and nut on the smaller side.

Thanks again for all of your responses.