for future reference
go to your plumbing supplier and get one of those neat little stainless steel brushes
one end is like a bottle brush the midsection will do the pipes outer wall
a quick twist back and forth on each and they are ready,
i use acid flux, not rosin, rosin is for electrical and not nearly as good as acid as a flux
flux both the pipe and the fitting, heat both from the bottom, and work the solder until you see it suck up
continue to play the heat onto the joint until you see it such up and weep out at the top of the joint, then
drop the heat and a quick wipe with a damp towel will finish off the joint and leave a professional look behind.
very easily done and quick,
my dad was a plumber and i have ran thousands of ft of copper along with fittings in my younger days.
as for repairing a joint after you have watered it...
disassemble the joint, clean well and prep it as normal
then stuff a piece of white bread up into both sections of the joint back about 3 or more inches
it will stop the water from dribbling down, and later will wash out of the fawcett no problem.
the last job i did was an old victorian home here in tacoma, it was a two bath 3 story home with basement laundry
and many, many feet of pipe and connections,, and no leaks.
btw, i have never tinned a connection, and quite frankly cannot see how you can do so and still get the connection back together
prior to finish soldering? the fittings we get here are far to close tolerance to allow for tinning.
bob g