Plumbing Compression fittings are used to connect two water pipes together without the use of glues or solder to create a watertight connection. Compression fittings are easy to use and only require minimul hand tools. Simply inserted the pipe into the comprssion fitting then the nut is tightened to press the compression ring (olive) into the seat, which in turn causes the seat to press against the pipe and compression nut creating a water tight seal. Compression fitting can be reused if a new compression right (olive) is used.