One problem I've got now is that the two ends going in to the elbow have solder on them. I've sanded them until smooth (they are still solder color, but smooth, is that okay?) and used a new elbow, and did that a couple times last night, but still no go. Is it okay to sand off the old solder and keep trying this way, or do I really need to start with all new pipe? It is easy to keep using new elbows, I've got plenty to spare... but I can't really cut back the pipe, not without adding yet another fitting (another coupler) which just seems like even more work, and eventually I'll have it cut back to the slab and not be able to continue.
The elbow fits well, nice and tight, just like all the others I did, so I have no idea why this one connection is giving me so much trouble. I did only do one other elbow though, so maybe I just got lucky on that elbow. Is there anything special you need to do when doing elbows? I've tried doing one end at a time, and also tried heating in the middle of the elbow and running the solder around both ends, one right after the other (while still hot, so they both cool/ harden at the same time).
I've read a lot about soldering... but, how long do you need to wait before testing? The pipe seems to cool pretty fast, so I've been testing within 2 to 5 minutes, is that not long enough? I kind of wish I could find an elbow with about 6" of pipe on each end, so I wouldn't have to worry about messing up one end while working on the other.