Galvanised pipe is durable, but plastics like polyvinyl chloride (PVC) are much easier to work with for the average do-it-yourself plumber. PVC pipe and fittings are inexpensive, readily available and easy to install with ordinary tools. When replacing water lines or making repairs, it is often necessary to join two different kinds of pipe. Connecting PVC to galvanised pipe isn't difficult. Of the different ways to make the connection, the easiest is with a simple PVC adaptor. One side of the adaptor is threaded into the existing galvanised pipe, while the other is attached to the PVC pipe with cement.
Use a wire brush to clean the threaded end of the galvanised pipe you are joining to PVC. Wrap four turns of plumbers tape around the threads.
Thread a galvanised in-line connector onto the pipe. Hold the pipe with one wrench while you tighten the connector with another wrench. The pipe should penetrate the connector a minimum of 3/4-inch.
Wrap four turns of plumber's tape around a PVC female-slip-by-male-threaded adaptor. Thread the adaptor into the galvanised in-line connector. Tighten the adaptor by hand until it is snug. Use a wrench to turn the adaptor an additional one to two turns. Do not over-tighten.
Use steel wool or fine sandpaper to clean the inside of the PVC slip adaptor and the end of the PVC pipe you are installing. Apply PVC primer to the inside of the adaptor and the outside end of the pipe.
Apply PVC cement to the adaptor and pipe. Quickly insert the PVC pipe into the adaptor and hold it in place for a count of ten.
PVC is best used for cold water supply lines and DWV (drain, waste and vent). For hot water lines, use CPVC instead.
Although they are available, don't connect PVC female-threaded adaptors directly to the male threads of a galvanised water line. The connector may split, and will eventually leak because the two kinds of pipe expand and contract at different rates.