I'm just a DIY homeowner but I can offer 2 bits of advice when soldering that I haven't seen listed here. One that drove me nuts and the other I just recently learned. Drove me nuts: When you cut a piece of copper, look into the cut end. I once had a defective piece of copper pipe that had a very small section of the wall that had a "channel" in it. So if you looked into the opening of the pipe, the wall was 1/16th of an inch thick(just a number, not actual) but there was one small section that was only 1/32 of an inch thick. The channel was too big to take the solder. Took me 3 tries before I figured out what was going wrong. And yes it was in an uncomfortable position to be soldering. Damn Murphy! The learned aspect was to wipe your solder joints with a dry rag not a wet rag. A wet rag can cool your solder joint to quick creating a "Cold" solder joint. The experts here can confirm or deny.