Fiction doesn’t generally spend a lot of time on what characters do in the restroom. I’m all in favor of this: a few years ago I read a bestselling fantasy novel that shall remain nameless, and I swear you could have made a pretty solid drinking game out of taking a shot every time the author mentioned characters peeing. By and large, I’m happy to assume they take care of their business offstage; I don’t need to see it happen.
But I’m still going to talk about it as a worldbuilding matter, because even if you don’t show the act of elimination, the question of where people take care of that can be relevant to the story.
Our list of terms for this is well-night endless: toilet, bathroom, restroom, ladies’ or men’s room, lavatory, loo, water closet, jakes, necessary, latrine, privy, boghouse, outhouse, house of office — that one’s Elizabethan — and more. Many of those are very much euphemisms (like “restroom,” from the days when the ladies’ facilities had an actual lounge to rest in), or else once had other meanings (like “toilet” for one’s general grooming process). And the euphemisms are culturally shaped, too: in Japanese one can call it the “hand-washing place” (otearai), but you’re unlikely to hear “bathroom” or equivalent because they put the bath and the toilet in separate rooms.
Presuming you’re at a higher level of sophistication than merely ducking behind a convenient bush, it usually offers you something to sit on. Aboard a ship, or in a medieval castle, that “something to sit on” is basically all you got: waste simply fell into the sea or down the castle wall, which I suppose in the latter case helped to deter invaders. Shipboard toilets are still called “the head” because this spot used to be in the bow or head of the ship, where it would overhang the water more, and the wind was more likely fling everything forward rather than onto the hull. In castles the term was sometimes “garderobe,” supposedly because the ammonia permeating the air would repel pests from clothing hung there.
But we can and have done a great deal better than merely sticking our butts out over open air or water. This doesn’t require sophisticated technology: more than four thousand years ago, the Indus Valley Civilization had toilets that fed into a system of sewers, and some of those systems included flowing water to help carry things away. You also find that on Skara Brae in Scotland, from a similar time period, and a little later in the Minoan, Egyptian, and Persian civilizations, and later still in the Roman Empire.
The Roman examples raise another point of interest, which is the idea of public toilets. These have come and gone throughout history: Rome had them, but they mostly fell out of fashion in the medieval period, then started to come back with improvements in sanitation in the Victorian period. You would think they’d be an idea everyone supports, when the alternative tends to be people relieving themselves in the streets — just take a stroll through downtown San Francisco to see the unfortunate results of that. But as with any public facility, there’s the question of who’s going to pay to keep it clean and well-maintained, and such places can become locales for crime or sexual activity. I can’t find the article anymore, but I recall reading about quite a lot of pearl-clutching in the United States over the prospect of <gasp> ladies using public toilets; it took quite a fight by the sanitarian movement to make those widely available.
Back to private use: for a long time, the main alternative to the open hole or the sewer toilet was the chamber pot, sometimes called a close stool, or a whole host of other terms. You find these all over the world, and especially in bedrooms: rather than getting up and stumbling through the dark and cold (in an era where lighting your way required more than just flicking a switch), you would take care of your business with the covered pot you kept under the bed. In the morning, you or your housemaid would empty its contents somewhere, whether that was into a cesspit, a special drain, or the street.
And until the invention of the modern flush toilet, those were basically your options. Elizabeth I had a primitive flushing design gifted to her by her godson Sir John Harington, but it wasn’t until the late eighteenth century that we started to get something you or I would recognize today.
There’s also the question of how people cleaned themselves afterward. Needless to say, they didn’t bother as much as we do with hand-washing; germ theory made a big difference there. But wiping one’s butt is a more obvious step, and we’ve used a wide variety of things for the purpose. Once paper became relatively cheap, that was popular, though purpose-made toilet tissue came later in most places that weren’t China; otherwise ordinary paper got used, as with the cut-up pieces of newspaper you sometimes see in movies with old Western outhouses. If you could afford fabric, that was nice; otherwise nearly anything flexible would do, whether it was leaves, grass, moss, ferns, seaweed, fruit skins, or wood shavings (watch out for splinters?). Or not so flexible: seashells, corncobs, and stones have all seen use. The Romans notoriously used a sponge on a stick — a communal one. (At least they put it in a jar of vinegar between uses?) Or just your hand . . . which is unfortunate when you remember that part about not washing one’s hands afterward, though in truth most people would at least rinse it off, even if they didn’t use soap. And quite a few cultures consider using water to be the optimal solution anyway, which is why we have inventions like bidets.
So where does this become relevant for storytelling? All kinds of places. If there are public toilets, that will make a difference in how the streets smell, both when considering overall cleanliness and the stench when passing by such a place. A character who takes care of the necessities with a close stool in the bedroom will not have the same midnight encounters as the one who leaves to use an external facility. The presence or absence of sewers and hookups to individual houses will affect everything from public health to how a thief might break in.
I don’t generally need authors to give me large amounts of detail on where and how their characters defecate and urinate. But taking that into consideration when imagining the world isn’t the worst use of one’s worldbuilding time.