I have an old 150 year-old farmhouse in rural Miss. which is occupied intermittently. It is heated with gas space heaters in various rooms, all served by a propane tank about 20 feet from the house. The tank and plumbing has been in location for at least 50 years (as long as I can remember) and I wonder if it should not be replumbed. I have not been able to locate any leak, but whenever we turn the tank back on after a period of disuse, it takes a while to get the heaters to light, as if air is in the line. The line from the tank is copper tubing which goes into the ground and emerges under the house where it converts to ½” iron pipe. From that point it goes from room-to-room by iron pipe. If I were to re-plumb this, what would be the best products to use? I would be working overhead in a crawl space, so black iron pipe would not be my first choice, although I have threading and cutting equipment. I would think flexible tubing of some sort would be the easiest to use in those surroundings. Any suggestions would be appreciated. Keep in mind the underground run from the tank to the house. Thanks, Thiggy