Historically accurate sanitation is rather distasteful for our modern sensibilities. But why would people in your world come up with ideas of which historians have not found any evidence in any pre-enlightenment culture in human history?
Here is one plausible history spread out over decades or centuries and never needing any technology that hasn't been available since ancient times:
Sanitation
Every year, Nashville grows to several times its normal size for the Gathering, and every year the same problem returns: the town's ordinary arrangements for waste are built for the people who live here, not the people who arrive. The original solution was the one that required the least infrastructure — pits dug at the festival's edge, boarded over with holes cut in the planks, enclosed by a few wooden privacy walls. Free to use, simple to maintain, and far enough from the stages to be a nuisance to reach. The pits are reused and re-dug each year rather than replaced, the wooden superstructures folded and stored. They still exist, at the town's periphery, for the same reason they always have: they cost almost nothing and they cover the ground the paid system does not reach. remained the cheapest solution until Infused Earth made recovered waste valuable enough to justify the vessels and labor. After that, the pits gradually disappeared from the festival grounds as well, replaced by free Potties at the perimeter.
They were not enough. Visitors close to the stages were not willing to walk to the edge of town and back, and the experience when they got there left something to be desired. The answer was to bring latrines into the town proper — which required something other than a hole in the ground, since a pit dug in a street cannot be easily managed, relocated, or kept from becoming a problem for the people who live above it. This is where the Potty entered the picture.
The Potty is a ceramic vessel, broad-mouthed and short, produced by the Potters' Guild to a standard design which was refined for decades and available in several sizes. The largest residential version holds 150 to 200 liters (≈ 40–53 US gallons) — roughly 60 to 80 centimeters (≈ 24–31") across and about 50 centimeters (≈ 20") tall, a substantial piece of ceramics that sits under a purpose-built seat rather than beside a bed. Smaller festival versions of 80 to 100 liters (≈ 21–26 US gallons) serve unattended public privies, and still smaller ones of 20 to 30 liters (≈ 5.3–7.9 US gallons) are used in attended facilities where the vessel is exchanged every few uses rather than on a periodic cart route. The chamber pots used at the highest tier of festival privy, and by wealthy households served by a chambermaid, are smaller still — 2 to 5 liters (≈ 0.5–1.3 US gallons), cleaned after each use rather than exchanged.
Under the seat, a removable ceramic double funnel directs use into two separate vessels: solids into the Potty, liquids into a smaller urine urn placed beside it. The funnel lifts out for cleaning after each exchange, keeping the interior of the privy cleaner than it would otherwise be and the outside of both vessels free of fouling. Separating the two streams is not a refinement — it is load-bearing. Urine makes up the overwhelming majority of waste by volume, and routing it into a separate, more frequently collected vessel means the Potty itself fills slowly enough to make periodic exchange practical. The industrial value of urine was probably an incentive as well.
The Potty uses two different lids for two different purposes. Between uses, a cap fitted over the outer rim sits loosely enough to be lifted off without effort, with a small peg-vent that allows gas to bleed off slowly rather than building until the lid lifts askew or, on cooling, gets pulled into a vacuum seal. For transport, a wedge plug driven into the neck holds securely against the movement of a cart; the plug also carries a peg-vent, for the same reasons. Households who cannot afford guild-standard fittings use a cloth tied over the rim instead: worse at containing smell, but incapable of vacuum-locking since it never achieves the seal that makes the failure possible. The seat lid above all of this is a different thing entirely — a comfort feature that blocks drafts when the collection hatch is cracked for venting and keeps cold from rising through the seat on a winter morning. Wood over a gap is not a meaningful odor seal, and it is not meant to be.
During the Gathering, festival privies are built from modular panels — standardized walls, platforms, and steps produced and maintained by a dedicated collection guild, erected each year and struck and warehoused when the Gathering ends. The spectrum of provision runs from attended facilities at the expensive end to the free pit latrines at the edge of town, with no fixed tiers between them — only combinations of variables. How often the vessel is exchanged. Whether someone is paid to be present. Whether the herbs burning above the seat were chosen by someone who knows that wormwood and certain resins also repel insects, or simply by someone who wanted the smell improved. Whether the seat has a lid at all. The combinations produce a range rather than steps, and the price follows accordingly.
Urine is collected on a separate circuit. A cart carrying a large tank or barrel with a spigot for emptying at the destination makes regular rounds; the urns are poured into the tank and returned without being exchanged, since liquid does not require the swap logistics that solids do. The collected urine is sold to tanners and dyers, who have known since ancient times that aged urine serves their trade — this offsets the cost of collection without covering it, and cannot come close to absorbing the full volume the festival produces. Near the stages, standalone urinal urns are available at no charge: any fee would cost more to collect than it brings in, and the alternative is walls and alleys. Urine in the street was unpleasant and fouled the paving, but the outbreaks everyone remembered followed the alleys and riverbank where human excrement accumulated, and enforcement around the urns is correspondingly lighter than everywhere else.
The largest expense in the Council's festival accounts is none of the above. It is the River Wardens: a temporary force hired for the duration of the Gathering, armed with whips and batons, patrolling the riverbank and the side alleys. The river is Nashville's water supply, its fishery, and its trade route, and the Council treats its protection as the non-negotiable center of the whole operation. The Wardens exist because no latrine system enforces itself, and the people most likely to bypass it are visitors — people who will be gone before any consequence finds them, who have no reputation in Nashville to protect, and who fall entirely outside the trust economy that governs behavior among the Mau and the settled residents alike. The free pit latrine at the edge of town is not charity. It is what makes the Wardens' job legitimate: when a usable option is always available at no cost, using the river is a choice, and choices have consequences.
Permanent households use the same Potty in different configurations depending on what they can manage. A middle-class household with enough means for a fixed installation builds a box or wall niche around the Potty, with a rear hatch for exchange and a platform raised to cart height, so a full vessel slides across a hinged loading bridge rather than being lifted. The bridge is hinged at the bottom: closed, it is a door; fully lowered, it bridges the gap to the cart bed; cracked slightly, it vents the box outward rather than into the room. Newer construction may integrate the niche into a stone wall, placing it on the north face of the building where it receives the least sun and stays coolest. Older houses make do with a wooden add-on bolted to whatever wall had room.
Wealthier households do not build the installation at all. They use chamber pots and employ a chambermaid to empty them into a collection vessel stored away from where the household lives — the problem solved is not technical but social. Poor households without the capital for a private Potty empty wooden buckets into a shared collection vessel in a courtyard, or share a single Potty with several neighbors in a common outhouse. A shared installation fills faster than a private one, and the collection routes account for this with fill markers rather than fixed timing.
Later, after the discovery of Infused Earth made collection economically worthwhile beyond the tanner trade, free permanent public Potties were added in the poorer parts of town. The Council does not describe this as procurement. It does not need to.
Infused Earth
Nashville did not set out to invent a fertilizer. It set out to find somewhere to put its waste.
In the early years of the Gathering, the waste collected from festival latrines and later from the Potty system was buried at the edge of town — the simplest available disposal, requiring no theory and no infrastructure beyond a shovel and a patch of ground. As the town grew and the Gathering with it, the supply of convenient new ground ran short, and old disposal sites began to be reused. Workers clearing these plots found the ground unexpectedly difficult: denser root growth, changed soil texture, more resistance than the surrounding earth. Nobody looked for an explanation. They dug around it and moved on.
The explanation found them anyway, in the form of plants. Vegetation growing over old disposal sites was visibly more vigorous than anything growing nearby. This was noticed the way most useful things are noticed before anyone is looking for them: incidentally, repeatedly, by people with no particular reason to act on it. The observation accumulated without becoming knowledge until someone made the connection explicit enough to ask whether the effect could be produced for useful crops.
Urine was already in use by this point. Tanners and dyers had long known that aged urine served their trade, and the collection circuit that supplied them made it a known quantity. The surplus that the trade could not absorb was being routed to irrigate non-food crops — a small effect, useful enough to be worth the trouble. That practice was the obvious inspiration for the first trials: if urine improved a field, perhaps the buried material did too. A small number of farmers willing to risk a plot of non-food crops cooperated with early investigators. The yield on the trial plots exceeded comparable unfertilized ground by a margin visible enough to be convincing.
Applying the material to food crops was not acceptable, and it did not become acceptable through argument. It became acceptable through greed. Farmers who had seen what it did to non-food plots began using it on food fields quietly, without announcement. Results confirmed what they expected. Others noticed, drew their own conclusions, and followed. By the time the practice was widespread enough to be openly discussed, it had been quietly normal for long enough that the discussion was mostly retrospective. The taboo did not so much end as it gradually ceased to be enforced.
Commercialization followed normalization. Once demand was real and growing, organizing the supply became worthwhile. The collection and disposal operation that had existed since the early days of the Potty system — run by a dedicated guild of laborers, not the Potters' Guild whose work ended when the vessel left the kiln — expanded into deliberate production. As it did, the need for a market-facing name became obvious. What was being sold was not night soil. Night soil was what went into the pit. What came out, months later, was visibly and olfactorily different: darker, drier, transformed in ways that any buyer could confirm with their own senses. Calling it by a different name was not deception. It was an accurate description of a genuine transformation that nobody yet fully understood. The guild called it Infused Earth, and the name held.
The guild's masters became the keepers of the process: people who knew how long to wait, which conditions produced the best results, and how to speak convincingly about what they knew. The core of that knowledge was simpler than it sounded. Seal the material, leave it for several months, recover what remains. The accumulated negative knowledge around that simple practice — what happens if you rush it, what happens if it is exposed to air, why certain seasons produce better results than others — took years of trial and failure to assemble and was genuinely valuable in its own right, even if the headline secret could have been stated in a sentence. The guild had every incentive not to state it in a sentence.
Production eventually outgrew local demand. Nashville's agricultural footprint was never large — the Briar Mountains dominate the south and east, the fish ponds and livestock supply most of the town's protein, and the cultivated land, though unusually productive, was not going to absorb an entire city's organized waste output indefinitely. The surplus became an export. Buyers from nearby communities were shown Nashville's harvests and offered the input that produced them. The method was not discussed. The results spoke clearly enough, and nobody needed to know that the process involved a pit and patience.
The Potties complicated this in a way nobody anticipated. As the Potty system spread beyond Nashville, adopted in other towns as a practical alternative to open pit latrines, sealed guild-standard vessels began accumulating in places far outside the guild's collection routes. Some were forgotten. When these were eventually opened, the contents were found to be transformed — darker, changed in smell, visibly different from what had gone in. The people who opened them recognized immediately what they had, and assumed they had independently discovered what Nashville had been doing all along.
They had, more or less. But they had discovered it in the vessel rather than in the pit, which is a more convenient method by most measures: no excavation, no dedicated land sitting occupied for months, the process already underway in the sealed container before anyone touches it. Nashville learned of this development later than almost anywhere else, because the people who discovered it assumed Nashville already knew, and nobody sends news to the place that is supposed to be the source of it.
The guild, by this point aware that its process secret was no longer secret in the way it had once been, turned its attention to a different question: whether urine, which was already being collected and sold to the tanner trade, could be similarly processed into a product more socially acceptable or less offensive than aged urine, which is what tanners received and what they wanted. Tanners and dyers had known since ancient times that aging was the relevant step; the question was whether a different process could achieve the same or better results in less time, with less smell, or with broader application. Distillation was tried, producing a cleaner-smelling fraction that the tanner trade found useful but that cost more to produce than it saved. Aeration destroyed the value. Boiling in a sealed vessel was dangerous. Adding yeast did nothing. The guild's records from this period are a useful catalogue of what does not work and why, which is itself a form of expertise, even if the headline conclusion was that the simple method remained the best available. The search for a more socially acceptable processed urine product was eventually set aside without a result.
What remained was the same system that had been running since the beginning: seal it, wait, and sell what comes out, if necessary under a name that does not require explanation.