I am curious what the difference is between Schedule 40 & 80 pipe? And where/when is it used? Also if someone could also help me regarding Class 200 & Class 315 pipe, and Solvent Weld pipe I would greatly appreciate it. Thanks.

Rather than explain I'll just give you some reading. Schedule 40 is thinner than 80 and used fro drains rather than supplu. http://www.harvel.com/pipepvc-sch40-80-dim.asp