Anecdote ahead: I put my dog to sleep last year, and as she slipped away, she shat. One turd fully out, and by the time she was gone, she had another one poking out.
It doesn’t happen a lot, but it most certainly happens. I have put down a lot of animals, almost all by lethal injection. It’s very difficult to put a number on it, but I would say that maybe 5-10% of dogs I put to sleep pass faeces during or immediately after. Often older dogs, and usually cases that have a general muscle spasm as the drug takes effect - which is generally more common in older, debilitated patients. It seems likely that these are patients that have had reduced mobility and have had less opportunities to evacuate their bowels prior to coming to the clinic. The amount varies, but it’s usually that of a normal bowel movement.
Urinary incontinence is far more common, maybe as many as half leak urine, and it happens a little bit later in the process, usually after I’ve had time to auscultate the chest or when agonal breathing stops, sometimes much later when the body is moved or handled.
As other have pointed out, this is plainly false. Maybe, Joe, you should try fasting for a few hours to give your digestive tract a rest.
Am I the only one who could the hear the sarcasm dripping off this post?
If that’s the case, mea culpa.
If I’m wrong, I’ll be back later to PALATR. 
In cancer cases, I would expect a fair number of them to have been on opiates, which are constipating.
When my uncle was dying, that’s what he complained about - not the pain, the constipation.
Regards,
Shodan
Once again, I did not say it was a “common occurence” but that it would be “common knowledge” (ie. known by many people that it does, in fact, occur) at that particular point in time.
Occurence does not = knowledge of.
Did you mean “dripping off the post-erior”? 
Proping open the sphincter long enough for someone to die of malnutrition would take days. Maybe you should take a closer look at diarrea, the condition. Since the body absorbs most of it’s nutrition from the intestines, the inability to retain that nutrition for any length of time would eventually result in death. The subject would die from lack of nurishment (aka malnutrition) and or dehydration without medical intervention.
The statement, “If one props open the sphincter, there’s a constant flow of feces until the subject dies of malnutrition” is correct.
Shoving solid objects up your egress would still allow the sphincter to seal the opening. Inserting a hollow tube and leaving it there for a week will result in death.
I’ve watched two dogs being put down (both mine) and we stayed a long time in the room after their death. Neither had any incontinence, either urinary or otherwise.
One did take a deep breath 10 minutes after declared dead however. The doctor immediately assured us it was a reflex. But it sure as hell sounded like a death rattle to me.
I also watched my grandmother die and there was no evacuation of any kind. Of course she hadn’t been eating or drinking much, we were all pretty much just waiting for her to go.
The anal sphincter isn’t there to ensure the bowels draw enough nutrients. It’s to keep you from constantly shitting yourself. Peristalsis ensures that food progresses slowly enough through the bowels; very little is being drawn from it by the end of the large intestine; in fact, the stuff being absorbed is mostly water at that point.
As a vet, I am more familiar with diarrhoea than I would have liked. Diarrhoea and faecal incontinence may occur together, but they are two very different issues.
Most nutrients are absorbed in the small intestine, the large intestine mostly absorbs water. It is true that severe diarrhoea leads to dehydration and electrolyte disturbances, which can be fatal if untreated. Nutritional malabsorption is also an issue. It is, however, entirely possible to have diarrhoea for a very long time without dying from malnutrition. That aside, an open anal sphincter does not increase the amount of faeces passed, or even the frequency of defecation.
I have managed faecally incontinent patients for years. Some are spinal cases, some have had rectal surgery due to tumours and have had the rectal sphincter damaged or completely removed. They pass faeces involuntarily, not at convenient times, but it does not flow continuously even if they have severe diarrhoea. It is not easy to live with, and it is something few dog owners would choose to put themselves through, but it is not a life-threatening situation for the dog and some of them seem to have a pretty decent quality of life.
I have treated dozens, if not hundreds, of lambs that are born with no rectal opening. The treatment consists of cutting a hole and letting the edges heal. They are faecally incontinent for as long as they live, which is usually about six months before they go for slaughter. They pass normal faeces. If the hole isn’t made big enough, they will get constipated - the artificial opening is much less elastic than an anal sphincter.
As for inserting a hollow tube - I have done it. It’s one way of treating an irreducible rectal prolapse in young pigs and cattle. (Insert tube through the prolapse, tie off the prolapse with a tight nylon band, cutting off the blood supply. Wait two to three weeks for the prolapsed portion to die off, the hollow tube allows faeces to pass through. Eventually, the dead prolapsed tissue falls off along with the tube, and you’re left with a shiny new hole. It’s pretty amazing.) The procedure doesn’t always work, but when it fails, it is due to constipation rather than diarrhoea.
Your scenario of “insert tube, watch patient die from malnutrition” would work if the tube extended far enough up - the length of the entire large intestine and most of the small intestine, that’s one hell of a tube. If you bypass most of the digestive tract, nutrients cannot be absorbed. Death would follow. But it would be from dehydration. It takes a while to starve to death.
Seconding the “spinchter tone is not related to diarrhea, nor decreased sphincter tone would result in diarrhea”, “even with decreased sphincter tone, feces produced are not the same as diarrhea”, and “it takes a while to die from starvation” (the last one, sadly, I have to deal with on a semi-regular basis).
Thanks for the info.
I have been a receptionist in a Vet’s office for 2 weeks now and the doc has had to euthanize 6 animals in that time (dogs and cats). She will not euthanize animals that aren’t sick or that can be treated (unless it’s required by animal control) so all of them were sick and at the ends of their lives. Only one of the 6 pooped. I asked her if it was common (at that point, it was only the second since I started) and she said that it wasn’t common but that maybe 1 in 10 would do it and it was much more likely if they were already suffering from digestive issues.
As I mentioned upthread, an ostomy (colostomy or ileostomy) bypasses all of the anal sphincters entirely. People live without anal sphincters controlling their stool output for decades.
I’ve bathed a few freshly dead people. Most of them were in the hospital basically on death watch. Maybe one in 10 had has some fecal incontinence, usually only a tiny amount. As was said upthread, dying patients are rarely eating heartily plus they are usually on pain meds, so their bowels are usually more bound up than loose.
Some people with colostomies still have a section of bowel attached to the rectum, that produces and expels mucus.
Human bodies are complex.
I was present at my mother’s death from cancer, and she had a death rattle. I thought at first it was the sound of condensation forming in her breathing tube, but when I took the tube out of her nose to clear it, I saw that there was no water in the tube and realized that the sound was coming from her mouth (her breath). It sounded…just like water crackling in a tube, or a little like carbonation popping. She died just minutes later.
She didn’t void her bowels when she died, either. Probably because she hadn’t eaten in a few days. Her hospice nurse had tried to give her an enema the day before and was surprised to find that there was nothing there.
I don’t know how common it is, but I plan to do it when I die.
Now I understand why some inmates on death row order really ridiculously big last meals! Kind of a final “fuck you” to the world.