On Oct 23, 9:57 am, wrote:
I'd cut the pipe back and add a coupling. You say you keep sanding
the used pipe ends and get it to clean solder, but the problem may be
beneath the solder. For example, if the pipe was not initially
properly cleaned and fluxed, the problem may be under the thin solder
coating that is left, where there is some contamination causing
problems again each time it reflows.

I'll have to do this if I can't get it after several more tries. At
least then I can do the elbow part on my workbench, where I can easily
get to all sides and rotate the part as well. Then do the coupling
inside the wall, where it is harder to get around to the back side...
but I've already done two couplings inside the wall, so hopefully this
one would also go easily.

The other choice is to sand off all the solder on the end of the pipe
down to bright copper.

I'll try this. I just don't want to sand too much, and end up making
the pipe weak. It does seem like I should be able to sand just a bit
more though, until the solder color is gone. The solder only bonds to
the surface of the pipe, right? So the pipe should stay the same
thickness as long as I only sand until the solder is gone.

They also make them for
use on the outside of the pipe and work much better than sandpaper.
They look like a doughnut and you just rotate it around the end of the
pipe.

This is the tool I have, love it -- as much as one that is starting to
hate plumbing can love any kind of plumbing tool. At least with the
masonry and woodworking projects I do, they will not flood my house if
done incorrectly.