Is it normal for a P-trap to still leak after replacing the washer?

You definatly don't want to use pipe dope or Teflon tape on those plastic slip-joint threads. Those threads aren't what acutally seals the connection; the **poly washer** does all the work. If you put dope on the threads, you're just making it harder for the nut to seat properly, and some oil-based compounds can actually degrade the plastic over time. If it’s leaking, it’s almost always a mechanical alignment issue rather than a thread problem.

Take the nut back off and look at the plastic washer. The tapered or beveled side needs to be facing toward the wall, sliding into the hub of the pipe. If you have it backwards, it’ll never seal no matter how hard you tighten it. Also, check the wall pipe itself for any deep scratches, burrs, or leftover glue from the old setup. Even a tiny bit of grit caught in there will cause a slow drip right at the top of the joint.

Another common culprit is the **trap arm** not being long enought or being out of square. If that pipe only goes into the wall adapter by a tiny bit, the washer doesn't have enough surface area to grab onto. It needs to be seated squarely. If the P-trap is pulling down or sideways becasue the sink tailpiece is slightly misaligned, that tension will create a gap. Try loosening the other nuts on the trap to get everything sitting neutral before you tighten that wall connection. Just get it hand-tight and then maybe a quarter turn with pliers. If you go beyond that, you'll just distort the washer or crack the nut. Glad you found the group helpful; we try to keep it useful here and avoid the gatekeeping you see on other boards. Just don’t ask anyone about **wax rings** versus the rubber ones unless you want to see a real arguement start.

Wait, now I’m curious about the wax ring thing lol. I didn't realize there was a 'civil war' over toilet gaskets. Is one actualy better or is it just personal preference?

Also, regarding the slip joint, is there a difference between those clear rubbery washers and the hard white ones? My kit came with both and I wasn't sure if one was better for the wall side. I went with the hard white one but I'm wondering if the softer ones provide a better seal if things aren't perfectly straight.

Stick with the clear rubbery ones for the wall connection if the pipe has any nicks or scratches. They squish down and seal way better than those hard white nylon ones. Those white ones are standard but they're super unforgiving if your alignment is even a hair off.

As for the wax ring debate, most old-school guys swear by wax becuase it never fails to seal if you set it right. The rubber or foam ones are basically for folks who are afraid of the mess or think they'll need to lift the toilet back up to shim it. Just get a deep seal wax ring with the plastic horn and you'll be golden.