Made a place-name generator for coming up with filthy Sewer settlements. Stuff like Runnelhurst, Drossgate, Swillminster... you can also roll twice on the first table! Muckslop, Cesstrough, Drecksluice etc. Throw in your regular ol' filth, muck, sludge & gunk, do a bit of mix and matching, and you're good to go.

As a general tip: anything with a guttural sound is really good for these kinds of place names (that's words with "U" or uh and ugh sounds, so stuff like muck/sludge/gunk). The letter "S" is also quite useful as it has quite watery, negative connotations (cess, sluice, slop, swill, dross, in the examples given here). In both cases you want to try and create a name that sounds ugly and damp.

Have fun!