Urban sand 

Urban sand is the term used to describe a cluster of trash with in an area or place that you don't want to pick up more or less liven up because life's better on a beach and eventually that's what are sands gonna be from all the excess rubbish in our oceans.

-Hey can you pick up this place?
-No I'm just trying to build up some urban sand for my soon to be beach house

Urban sand by TylerMelmer December 6, 2019

Urban Sand Castle 

When a public toilet becomes clogged, but people continually defecate into it, overfilling it with feces until the fecal matter stands on it's own weight in the bowl and over the toilet itself, often resembling a sand castle.

Man, did you see that sweet urban sand castle in the KFC bathroom?! It's getting huge !

Urban Sand Castle by Ballz Johnson September 7, 2016