PVC Fittings are the industry standard for connecting irrigation piping within a sprinkler system.  PVC fittings (polyvinyl chloride) are rigid pipe joints and come in various sizes and shapes.  PVC fittings are connected to PVC piping through the use of what is commonly called PVC glue.  Though it is regularly called glue, it is actually a solvent which once applied causes a chemical reaction to occur in the PVC which softens or melts the plastic.  This allows the fitting to be basically welded to the piping creating a permanent bond.  The use of excess glue during this solvent welding is not recommended as the PVC glue that oozes out of the joint once connected and weaken the piping at the connection.