PopSci hat einen ziemlich lustigen Artikel über Kokainschmuggler und wieviel Koks in einen Magen (für Langstrecken) oder in den Arsch passen. TIL Megarectum exists.
The maximum capacity of a normal rectum--meaning, before the patient is overcome by the urge to defecate--is about 350 to 500 mL, or about a pint in volume. That's a lot; the first urge to defecate comes at about 100 mL, so if you're storing five times that amount, you're probably pretty uncomfortable. But repeated stretching of the rectum can increase that size markedly. "We do know that it's not rare for people to have larger capacities," says Dr. Whitehead. "We have certainly tested people for whom it's 800 mL. With practice the capacity becomes larger."
The rectum is a fantastically powerful, stretchable part of the body. The problem I kept running into in trying to figure out how much cocaine you could fit in your butthole is that, well, there isn't really an upper limit. It's all about conditioning and practice. That said, let's take that 800 mL as an example upper limit. Given the density of cocaine hydrochloride, that converts to about 0.97 kilograms of cocaine, or very nearly the size of one of those big bricks you see confiscated on the news.