Abstract: An in-line pipe coupling comprising a joint housing which encloses a piston means having a standard diameter pipe section which protrudes from one end of the joint housing may be compressed and inserted into a small cutaway section of existing pipeline and then expanded to fit over the two free ends of pipe, forming a continuous water-tight connection. The slip joint may be utilized in conjunction with either a standard straight pipe coupling or a T-coupling or cross coupling in order to facilitate addition of one or more branch lines to an existing pipeline.