hi
Haha, sounds like there is info.
As for drainage tunnels, because the area is quite old and built on high ground between river valleys (Melbourne was very swampy in the eras before a lot of infrastructure was built) there's actually not a lot in that particular region. Maybe the tiny side pipes or end pipes.
Royal Park Psych Hospital used to have access corridors underground (my dad used to work there and claimed they were haunted).
The famous steam tunnel in the area is of course the one between Melbourne hospital in Parkville and the exhibition building (near Melbourne Museum). My workmate got to drive a truck through it regularly. It's very secure however! A friend took me in the old hospital ones in South Melbourne 30 years ago which were probably very similar.
If there is anything under the residential areas, the State Library or Melbourne Uni library might have some clues.