I am installing a new bathroom sink and it is leaking in two parts, at the faucet drain and at the p-trap. I will ask separate questions for each of these as I believe it is a different solution at both sites (where its leaking). This is all 1 1/4" plumbing. Here I will ask about the p-trap leak.
The installation looks like this:
Here is where the p-trap leak is occurring (at the junction between the p-trap and the drain/outlet (the long pipe going into the wall):
As you can see, this is a brass p-trap that I bought as part of a kit, and it only came with a nut (no washer) for the trap-outlet connection:
It might be hard to tell from that photo, but at the end of the outlet pipe, about 1/4" away from the end of it (where it goes down into the p-trap) there is a metal "lip".
I tried adding an 1 1/4" rubber washer over the lip but then I can't screw the nut down onto the trap threads. And (at least in my mind) it doesn't make sense to attempt to place a washer in the ~1/8" space between the lip and the end of the outlet pipe.
Does my installation look correct? Am I missing a washer somewhere? Why would this joint leak? I've unscrewed and rescrewed it multiple times, and tightened it considerably and it leak like a sieve.