How do I add a P-Trap to a copper drain?

Question

I started to get a smell in the downstairs bathroom and after ruling out the wax seal on the toilet it is coming from the sink drain. We are in a split level so technically its in the basement.

Strangely there is no P-Trap, just a drain that goes into the wall and I assume straight into the sewer line as the drain doesn't come out on the other side (a garage is on the other side of the wall).

Is there a reason for not having a trap?

The main question: How do I install one. I am quite handy and have no problems working with PVC but wanted to get advice on how I disconnect the copper (is it copper?) drain and what I would use to go Copper -->PVC (links to home depot welcome!).

I am assuming i use a blowtorch to melt any solder but want to check first as I don't usually work with copper. If it was a pressurized line I would call a plumber but I'm confident with guidance I can add the trap.

Answer 1

What size is that copper? You can get plastic p-trap kits in 1-1/2" and 1-1/4", and these can be easily connected to your copper via slip ring compression fittings. Basically they consist of a nut with a cone-shaped plastic washer, which when compressed by the nut squeezes against the (copper) pipe to create a seal. Usually these are only on the sink side of things and the wall side has glued-on plastic but you can use the compression fittings on both ends.

Here is a 1-1/2" Plastic p-trap

If you want to solder, a better solution than using a compression ring on the wall side would be to sweat on a copper x female adapter, followed by a male PVC adapter and a PVC trap adapter. Better yet if you can find one, just use a brass copper trap adapter like the following:

A less desirable but acceptable solution would be to use a fernco fitting to go from the copper to PVC, and then you can avoid soldering.