Rozemyne will take on even the gods themselves in her quest to rescue Ferdinand. She speeds to Ahrensbach faster than Steifebrise, and as the battle against Lanzenave commences, Georgine finally begins her invasion. To war!
It was pointed out in the past, that rather than individual accesses to the sewers, the temple had a communal disposal spot in the courtyard, to which the attendants had to carry the chamer pots. And seeing how even the orphanage director's chambers doesn't have a toilet (it was mentioned that it was Delia's job to empty Rozemyne's chamber pot), there's no way the basement of the orphanage would have one either.
The sewers might have been connected to the temple in the city remodeling in anticipation of large scale paper production. Not entirely sure if anything of the sorts was mentioned and even if it was I doubt Georgine would know about it (her information network inside the temple was likely cut off entirely before the city remodeling) but it's an option nonetheless.
The blueprints for the sewer remodel were drawn up by Sylvester's scholars, some of whom were in Georgine's thrall, so presumably she can have a very accurate map. But.. I suppose if Ferdinand did a final check & amended it to include the temple and then handed it directly to Sylvester, this scenario could happen. All that said, connecting the fresh water tunnel to the workshop wouldn't exactly be a doorway, and while the tunnel is empty there's no reason for any final connection at all.
I felt so sorry for her the entire about 10 minutes she thought something bad happened to Rozemyne. Poor girl was fearing the worst meanwhile Rozemyne is just passed out in a bed in Ahrensbach