Avoid using PVC
A few points:
PVC production is the largest use of chlorine gas in the world.
Chlorine production consumes enormous amounts of energy.
Chlorine production causes mercury pollution.
Hazardous by-products are formed throughout the PVC lifecycle.
By-products of PVC production are highly persistent, bioaccumulative, and toxic.
PVC is extremely difficult to recycle.
PVC is one of the most environmentally hazardous consumer materials ever produced.
Different grades of PVC have different melting points, flash and glass temperatures.
At 70-80 Degrees C (~150 F), most grades begin to soften and degrade in performance. This should be taken into account when building projects that involve any kind of direct or indirect heat, including hot water, etc.
(I've edited this post to contain more useful information)