Saying that it can be used for a water heater T&P relief discharge line is like saying one can use a gun to shoot oneself with - it's not recommended, but, sure, it *can* be done - just not a real good idea.

Not sure there is a law against shooting oneself either, I mean, who are they going to charge for breaking the law - the dead body? "Hey, you there, laying on the floor, you are being charged with discharging a fire arm in the vicinity of one's head, leading to and causing the death of oneself." Yeah, right.