Mostly speculation on my part, since I couldn't find any references to this specific technique in either of the two main reputable peer reviewed torture journals (e.g. Issues in Enhanced Interrogation, and Questioner: Journal of the Academy of Torture Professionals.) But I have to wonder if this technique would be as effective as the standard method of water torture. For one thing, I suspect the victim would be able to expel the fluids back out through the funnel. I think you'd need to introduce the fluids under pressure or have a one way valve or plug to keep the fluid in place. If there was enough water pressure in the funnel to overcome the back pressure of the victim's intestinal musculature, then I think you'd be more likely to rupture the intestine than fill the stomach. The intestine is long and bendy (about 27 feet long in total) and there's a pyloric sphincter-a one way valve-between the bottom of the stomach and the beginning of the small intestine, so the water pressure would have to overcome that to fill the stomach.Apparently one can fill a belly with water using a reverse technique ... who knew?
With that kind of water volume you'd also be altering the victim's electrolyte balance to the point of potentially causing organ failure, but I don't know if that would be an immediate effect.
And just a reminder--the victim doesn't breath through her south end, so she would not be experiencing the drowning sensation that is such a significant part of the water torture experience.
I've no doubt that filling someone's gut with fluid would be extremely uncomfortable/agonizing. Now very hot or very cold fluid would be a torture in and of itself, as suggested in one of the illustrations above, but my comments only apply to the idea of filling the stomach via enema.
All in all I'm going to suggest that this is a technique probably best not practiced by the average DIY'er in his home dungeon. Certainly not without proper supervision the first time or two anyway.
BTW, I have read that the "retired" Aztec elderly--those who had lived long enough to be allowed to do whatever they wanted--would give themselves pulque enemas. I've never tried it, even though I am in that age bracket, but I can imagine one could get spectacularly drunk and yet have very little stomach upset.
Kinda gives a whole new meaning to the expression "Party-pooper."