One of the problems I have when remodeling a kitchen or bathroom occurs when I have to sweat-solder new fittings into an existing copper water-supply line. It is almost impossible to get all of the water out of the pipes, and that leads to poor solder joints.
My solution is to drain the pipes in the usual manner — being sure to open faucets at the highest point in the system — and then use my wetvac to suck the remaining water out of the lines. This procedure requires a vacuum-nozzle reducer to ensure a tight fit and good suction (I use the plastic reducer that connects my orbital sander to its dust bag). Remember to vacuum both the uphill and downhill ends of the line. I find that after about two minutes the pipes are dry and ready to solder.
Peter D. Ellis, Needham, MA
Another little trick if the water is not coming out very fast is to stuff a piece of white bread in the pipe right before soldering. Once the water is back on, the bread disintegrates and doesn't damage anything.
This sounds like a good idea when draining the water lines for winter in the camp. In the past I've relied on gravity or an air compressor to clear the lines, but using the shop vac sounds a lot easier . . . now for the fittings . . .