This is a neat worldbuilding idea about adding weird and impractical cultural things to the societies you create. They’re not inherently unrealistic if you address the realistic consequences. Here is an amusing example:
(via: r/tumblr)
Weird Worldbuilding Idea
As an aside, this WAS actually the case in Morocco; and the pigeon droppings
WERE collected by people who were highly regarded for doing so. They were then made great use of; because there’s an enzyme cocktail in pigeon dung that does AMAZING things to leather. Moroccan leather is soft, supple and makes the finest leather furnishings and garments – and it’s all down to the fact that the leather is soaked for a while in pools full of pigeon dung.
So not only would your fantasy city be uncommonly clean, it would likely have an extremely successful luxury leather-goods industry and abundant agriculture feeding off of one of the primary waste products of the leather industry – the pigeon dung that has fermented beyond the point of usefulness to that leather industry.
Now, considering that the pigeons are quite literally the source of most of the city’s money-making trades and the primary source of fertiliser for their crops, I’d say it’s only natural for the people to see them as sacred, and for there to be laws preventing their wanton killing. Not to mention for the public purse to be feeding them, and even having dovecote shrines where they can rest at night, safe from harm. The city might even take its name from the dove, or a deity of doves; and members of the public would freely report ANYONE they caught harming a dove, as they know from whence their food and income comes, and they aren’t going to stand for anyone messing with it.
Now, while all of this is actually based on a factual truth in the real world, there’s no reason why you couldn’t arbitrarily decide a similar thing for something entirely fantastical. Maybe gryphon dung contains a universal mordant, fixing the colour of pretty much any pigment into cloth, and thereby allowing profoundly beautiful natural dyeing to create an esteemed textile industry. A similar mechanic would then evolve around gryphons in a major city or region as a result.
The point being: don’t leave a thing out because there’s too many real-world logistical issues that you can see. It’s a fantasy world – so let fantasy find a way to handle the logistics issues, and move on. And hey, you may well find a way through fantasy to use those logistics issues as a source of logistic strength and benefit – just as with the real-world example of pigeons.