I've recently (in last week) installed a urinal in a new basement bathroom.
Supplied with 3/4 from main house supply line by PEX and into a threaded drop ear elbow then threaded 3/4" copper pipe nipple with Teflon.
The output end of nipple is threaded and Teflon tape into control stop.
Plumbed rest of valve and it works...

But it leaks; as far as I can tell a slow drip from the drop ear and nipple inside the wall.

Did I mention it didn't leak when I had my black pipe with cap on it for a month?

Did I mention since it didn't leak I tiled behind the urinal already and covered up easy access to the drop elbow?

I've taken it apart 4 times now, re taped and installed to same results. I've also tightened control valve one more rotation, I may be able to go one more BUT I'm afraid to snap drop elbow off block behind tile/drywall.

If I'm left with no choice I'll take wall apart, but am I missing something? Is the black/galvanized pipe different than the copper (pipe pitch/taper/thread) so put the black back in? Do I try one more rotation?

Thank you... I probably already know the answer

Take it apart and re tape it and use some pipe dope too. All npt pipe thread are the same.

It's possible that the drop eared ell was made in one country, the iron nipple in another, and the copper adapter in another. The threads are likely not going to be exactly the same. First thing I would do is remove the copper adapter and use a brass nipple. Use a little dab of pipe dope atop the thread tape, it won't leak unless the drop eared ell is cracked.

Thanks guys

One mistake, it is a brass nipple.

I'll remove retape dope and install again.

I'm also thinking the decorative chrome nipple cover might be preventing a tight fit because it's a little long and interfering with each end of the drop elbow and valve.

The cover does NOT have to cover the entire nipple, just the portion that is visible.