Reheat Solder When You Can't Cut a Pipe
The best way to disconnect a soldered pipe is to cut it. But sometimes you can't—either because you can't get a cutting tool into the space or because cutting would leave the pipe too short to make a new connection. The solution is to heat the joint and pull off the fitting as the solder melts.
Have a wet rag handy and immediately wipe away the molten solder before it hardens. (Wear gloves to prevent burning your fingers!) Sometimes a quick wipe will leave the pipe ready for a new fitting. More likely, you'll have to scour off some excess solder with sandpaper or emery cloth before you can slip on a new fitting.
Replace Metal Drain Lines with Plastic
Metal drain lines under sinks look a lot more reliable than plastic. But plastic is better in almost every way. It's cheaper, easier to install, and easier to adjust or tighten if a leak develops. And unlike metal, plastic won't corrode. So when a metal drain leaks, often the smartest move is to replace the entire assembly with plastic.