I appreciate where you're coming from, and, yes, the worse that can be imagined is disastrous.
I hesitated before sharing my thoughts. Maybe I shouldn't have. And I certainly wouldn't want anyone to follow my 'advice' blindly and carelessly, and regret it.
But I will defend myself to the following extent: the jars I use were all originally filled with foodstuffs that weret over 100°c - the water I put in them will be in the 40°s. And these are jars that can withstand huge pressure: I can stand on them without them breaking or cracking (I do this on 'duplicates' of course) - and this is 90kg of very unevenly-distributed pressure. The pressure exerted by anal sphincter muscles is evenly distributed, and is neglibible (compare the experience of a man of 90kg standing on your hand with what your hand experiences when fisting).
I have used jars (amongst other things) for, I guess, over 15 years, and there has never been a problem.
I of course don't take that to mean that there can never be a problem, and you are correct to point out the risks. It's just that when the risk is below a certain level it becomes an acceptable risk. Like driving - there is a level of risk, but we can manage that risk, we can drive carefully, and let the benefits of driving outweigh the ever-present risk.
(for example I read about people using drugs whilst working their ass - for me that would constitute an 'unacceptable risk' - whether for physiological, psychological or social reasons - but I respect that those who do use drugs will have much more experience than myself, will do so cautiously and responsibly, and will be making a more rational calculation of the risks than I ever could, who has never been into drugs).
I am however grateful for your concern for others on this board, and for myself.