Why Sewer Dwellers? If so, is Deganwy on the list? Haven't checked it yet.
Because the Sewer Dwellers are the criminal organisation of caliban and other outcasts that lurk in Vallaki's sewers.
However, the Drain or Degannwy would not be on the list. Since they are not organisations, but settlements / places.
Just ask yourself, does this group have membership? In almost all cases that tells you whether it is an organisation or not.
Clans, tribes, minority groups, notable families, noble houses and small business ventures seem to be purposely left off the list.
If Degannwy is an actual society with membership it probably belongs on the list, but I don't think they are that kind of society.