softening
At the risk of sounding sarcastic, I'm assuming since YOU haven't experienced it, it COULDN'T possibly exist under normal conditions?
Steam? No 140 degree water will do the trick, and I've been involved in repairing many kitchen sink drains with tubular plastic lines that had softened, and, as a result, deformed or simply pulled apart at the compression fitting.
You WILL note that I also commented that finding QUALITY tubular products was a problem, indicating that if one could theoretically improve existing quality (longer insert lengths in compression ftgs), one may decrease the likelyhood of temperature failures.
It is my professional opinion that a sch40 drain assy, installed as I described is NOT a waste of money OR time, and , in fact, provides a superior (not inferior, as was indicated by another poster.....you?) installation.