This sounds very sexy, but I was wondering if there are risks even if you discount STDs. Say you are with someone you totally trust, have been monogamous with for years and have both been tested for STDs. The sort of relationship where you would stake your life on the other partner being faithful (well, this is more or less what you are doing in this scenario).
In this situation I wonder what the risks are from incompatible gut bacteria that one person has immunity to, but would be pathogenic in the other person? Does anyone have any thoughts on this?
Note that in a real-life medical setting fecal transplants are done as a last resort therapy for life threatening antibiotic resistant C. diff - so the risks of the transplant are much lower than the risks of not doing the transplant.
I don't think I'd be willing to risk this one under any circumstances BUT I do have an idea of how to accomplish a very similar thing without sharing any fluids:
1)take two flexible enema bags
2)find/make a stiff box just big enough to hold one empty and one full side by side.
3)take two people - clean both of their colons thoroughly
4)fill one partner with water from a third bag.
5)Place the box with the two bags slightly lower than asshole level of the two partners
6)both partners insert the nozzles from the "bags in a box", the full partner taking the empty bag.
7)The full partner will drain into the empty bag, putting pressure on the full bag and beginning to fill the partner who started off empty (especially if the full partner starts of a little higher to overcome friction). Eventually an equilibrium will be reached.
😎Now the fun can begin - e.g. sex where whichever partner is on the bottom gets filled from the partner on top, then swapping round to reverse the process.
N.B. using saline instead of plain water would be a very good idea here to stop excess absorption.
Inspiration: The "hydraulic analogy" componant of an electrical capacitor - look up hydraulic analogy on wikipedia if you don't know what this is.