A photo would be good at this point...

There is water forming at the top of this nut here



and and this one here





I think this leak is due to that broken ring that separate the rubber from it's slip nut...not pressing evenly.




I do see it is leaking on the back side here



but that's not timing the same...i didn't feel this drip until after the water appeared at the nuts.

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First, the black beveled ring is (almost) NOT a seal,
it's there to provide tension against the real seal,
The ring under the guys fingers in pic 3 of your diagram above.

In order for water to leak to the black ring, the water hasta
leak past the 'finger' ring.....
Check that ring again, and if not broken,
apply some plumbers putty to basin before installing drain.



....and don't put it on sooooooo tight !!

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so if I am correct in thinking here, the problem is at the big black washer and it is dripping on top of the other two areas he is pointing at, hence the confusion of where it is leaking..?

and while my plumbing ability is universally comical can I ask if there is a way to get a longer piece to go from sink to trap without two separate pieces with two separate nuts/washers/twisties, thus eliminating one nuts/washers/twisty?

and HOLY CARP...that last photo has a face staring back at me!!!!!
(and it dont look happy)


Actually that looks like the same type I just put in my basement...partly may need to make sure it that black part is in the sink fully....

That finger ring is the foam ring AmStan shipped to me above.



The tailpiece is only so long...hence the extension. So unless they make a trap that reaches up higher than normal, I believe this is the only way to do it.

I didn't even notice the face when I posted the pics. Guess you can now tell where the Mrs keeps me when I'm home.

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With the basin full of water, the foam 'finger' ring
should be doing all the sealing....

If it drips, it ain't !!

(With the exception of a teentsy amount
that will seep by the drain plug,
but that should go down the drain.

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Sorry to jump in so late here, but, in reading this thread, I'm confused. And, I've done a fair amount of pop up assembly installations.

Some assemblies do indeed use a 'foam' ring instead of plumber's putty to seal the topside flange in the drain hole. This foam ring is not the same as the anti-friction ring used between the black rubber beveled washer and the slip nut. As CC mentions, that ring is a thin plastic material and it simply allows you to tighten the slip nut against the bottom of the black washer without deforming it as you torque it. I've never seen this plastic ring break under tightening.

I have seen many issues with leaks at the top threaded connection, the black washer sometimes doesn't want to seal. In those cases, I take everything apart and make sure the hole in the bottom of the sink is round and doesn't have any chips out of it. Then, I insert the tailpiece, using the foam gasket or plumber's putty underneath the flange, for a seal. Often, I'll wrap Teflon tape around the threads where the black washer will fit, then, start the nut turning so I push the black washer towards the sink hole. Using a gentle touch, I allow the black washer to seat itself as I screw the nut home. This makes sure the washer is properly centered and seated. Now I'm ready to assemble everything else.

Using an extension on the tailpiece is very common and shouldn't be a problem. Make sure your plastic ferrules are in good condition and the mating pieces of PVC are clean and free of burrs or labels.

Sometimes, even after using all my tricks, the tailpiece will still leak at the top of the black washer. If I'm content that the drain hole is uniform and is not the problem, I'll start over with a new pop-up assembly.

Good luck, Bob.

In addition to the possibility of voids, the bottom surface is sometimes not flat and/or there are bumps on the surface which can make it impossible to seal without dressing it up to provide a flat sealing surface.

so if I've tightened up too much...breaking the friction ring...is it possible the rubber washer is now too deformed to seal? Or would loosening things up allow it to spring back?

Wonder if AmStan will send replacements for the friction ring and rubber washer......

Sometimes just loading up a leaking joint with teflon paste will seal the leak. I usually use in on the rubber gasket that goes on the bottom of the sink. Sometimes the sink drain bottom is not flat and smooth and it leaves a leak point at the rubber gasket.