A compression tee (or coupling) is pipe fitting that is used to join existing metal or PVC pipes together and are primarily used for connections that are underground.
To install a compression tee to combine two pipes, ensure that the pipe you are installing the tee to is firmly anchored in the ground and cannot move backwards and forwards. Ensure that you have the correct size tee for the pipe you are fitting it to; this will depend on the diameter of the pipe and the material the pipe is made from. Once you have the correct tee, shut off the water to the pipe you are connecting to and cut off a small section of the pipe being connected – this should be about half the length of the tee itself. Clean the pipe surface where you intend to attach the tee and tighten the nut or ring to attach the tee making sure that the rubber gasket is in the correct position.