How to you tap on the wall? For some reason it's always greyed out I also cant find a way to access the sewers
For the first one, it's probably just a more corruption thing. Was greyed out at first, then some time later I could tap, probably after the training that unlocks tip jar/service actions.
For the sewers, buy code reader from the mechanics shop and meet with nora about it, then buy the 17G scanner and place it until you find it points to the sewers. Give wallets to the chud king (at the arcade in the morning) so he trusts you, and then having done both Catherine will bring up wanting to enter the sewers when she talks to him. Buy the sewer gear, and you can enter the sewers. Hope it helps.