I haven't done anything nearly as impressive as either of these two stories, just re-moulded 4" PVC pipe into flat 1/4" sheets in a small electric oven (not household type). PVC sheet can be rather expensive, while drain pipe is cheap in comparison. So that was the reason. I have an old style Harbor Freight plastic welder that I used with a compressed air line, and a router speed controller to control both heat and airflow. I built a simple slit and grate spectrometer with that flattened plastic, some intact pipe and a couple of razor blades and a CD.
I've also built a dairy whey digester to produce methane with PVC pipe, but it required no molding of the plastic -- just conventional plumbing, so it doesn't count here.