Solvent welding is the process used to join two pieces of PVC together. When done properly the bond is extremely strong. I may write my own guide at some point, but for now you can see several different guides in the related links below.
related linksBurnt Latke solvent welding guide
advancedspuds.com solvent welding guide
instructables solvent welding guide
Oatey instructional videos
DoItYourself.com working with plastic pipe
IPEX online training course