Hi, I bought a 1820 Farmhouse that had some pretty shifty work done on the plumbing. My question is when replacing the plumbing going out, do I have to turn off the water. I am not replacing the plumbing from the well to the sinks/tubs. And is it better to use 3" or 2" pipe. It is the correct plastic pipe now, but it is a 1/2" and is causing a backup in our dishwasher. The washing machine drain is 3", and goes to 1/2" to drain into the seperate water well/grey water. Our piping is shaped like a "V" forcing our washing machine, sink, and tub water to follow 1/2" pipes one way filling up our dishwasher, then comes back and goes out to the water well/grey water. This is the plumbing I am going to fix and make one long pipe and connect each item to it.