"Do you really wish to know?" Spoilers from the books and/or games to follow!
The Salamandra hideout in the sewers is located in an old crypt. This hideout is variously known as the "fisstech lab" or the "Bandit's hideout" but whatever the name, it houses the main production line for the fisstech manufacture operation of Salamandra. It can only be access by providing the correct password, unless one is prepared to resort to violence.
It is run by Gellert Bleinheim, the local drug lord. He employs a large "staff" of chemists working day and night to produce the drug — I say "staff" because it is not entirely certain that these men are working there of their own accord. The raw materials are supplied by Bleinheim's brother, Roland from his operation in the swamp.