Sewer Music

I am not at all sure what the artist(s) Deaden The Pain meant by calling the just-released-today song, "Sewer Clown" (Electronica-downtempo, key of C-) but maybe he/she/they heard of the Los Osos sewer war? 
https://www.beatport.com/track/sewer-clown-original-mix/8672224

There is also an original mix of a song "Sewer Rat" (someone sounds very upset in a digestive track sort of way) by the artist Akcept (Dub step, key of D major):
https://www.beatport.com/track/sewer-rat-original-mix/8390756

How about "Septic Sludge" (by Kiro and Marshall Applewhite) for those of us yet to hook up (Techno, key of G# minor)?
https://www.beatport.com/track/septic-sludge-original-mix/7845917

However, if you go to the search box on Beatport and type in "sewer" (https://www.beatport.com/search/tracks?q=Sewer), a remarkable amount of sewer songs appear. And this is just ONE music website. What does it all mean?

(On a loopier note, here is a pun one! Here is a mellow sewer song, very California!)

Enjoy!