Waste Oil

The S'aue, while mechanical, require sustenance just like all other living beings. It just so happens that their sustenance is crude oil, which they must ingest on a bi-weekly basis for optimal operation.
  This, of course, necessitates that the oil that has circulated in their system for two weeks has to come out first before its replacement is put into circulation. This is referred to as waste oil, and an entire industry has formed around it.
 

Properties

Waste oil is, as the name implies, a waste product that contains the grime and debris that has coagulated into it from the tubing of the individual it has circulated in.
  In addition, the lubricants and additives in the refined crude oil that the S'aue consume spoil over time, which has an effect on the viscosity, scent and coloration of the oil.   Waste oil is instantly recognizable by its distinct, pungent stench that resembles the scent of muddy loam, with the stinging undertone of sulfur from the spoiling impurities in the oil.
  Ironically, the S'aue themselves do not perceive this smell as they are not capable of olfaction, which makes smugglers favor the railways of the S'aue Empire for moving the substance around Nascindor.
  Visually, waste oil is distinct from pristine crude oil via a slightly translucent brownish coloration, with visible detritus swimming in it.
 

Oil change

When it comes time for a S'aue individual to change their oil, they will use a siphon that slots into a connector port specifically designed for such siphoning. S'aue also ingest new oil through this same connector port.
  The waste oil is siphoned out of the system of the S'aue into a container, which the individual will then return to an oilmonger, a professional that will purify part of the waste oil and sell it back to the citizenry and aristocrats.
  The rest of the waste oil, the contaminated sludge that has no other use, the oilmongers sell to the Deficient at a discounted rate, who rely on this used leftover oil to keep themselves functioning.
 

Smog Season

At some point waste oil becomes so contaminated that it is useless even to the Deficient. Unfortunately, this usually happens while it is circulating in the system of an individual, meaning that function ceases for that individual.
  These "clots", as the sanitation crews refer to them, are collected and the nearly coagulated oil is drained from their systems before their chassis is delivered to a scrapyard. The useless leftover oil is then brought into incinerator towers, where it is burned once a month.
  This burning generates a cloud of smog so thick and pervasive that it hangs around the city or settlement for an entire week, which is colloquially referred to as "Smog Season" by the non-S'aue residents, who will have to retreat into their homes for the week or risk severe health consequences. The aristocracy, whose penthouses are often situated above the smog, are naturally unperturbed by the practice.
  While it is preferable that the S'aue dispose of waste oil in this manner rather than dumping it, the smog released from these burning events is not without its ecological impact.
  Dignitaries from the city-states, especially those of Glarithian descent who have come to appreciate beauty and nature, are working with like-minded S'aue researchers to find alternative disposal methods.
  The S'au Empire has a different view of the problem, and seek to find or invent a replacement for crude oil entirely, effectively removing the problem at its root if they are successful. So far there has been no noticeable progress on this front.