If someone has persistant diarrhoea that doesn't respond to antibiotics, one solution of last resort is to give them a fecal transplant to replenish good bacteria in their intestine. Yes, that's right, they transfer someone else's poo into them.
Whose? Apparently someone they live with is best because this gives a match for the balance of bacteria creative by diet and environment. So generally a spouse or family member. I guess a flatmate would do. Kinda weird tho.
How? Well they used to do surgery on the colon to insert it, nowadays they find it is much quicker and less invasive to put a tube down your nostril. Yup, they pour poo down your nose. Someone else's poo. As a medical treatment.
We live in interesting times.