So I got out of the flooded district and made my way back to the Hound Pit Pub. I've worked my way around and met with Piero... Apparently I need an empty whale oil canister to set up their modified pylon, but there isn't one in his workshop, in Corvo's room, in the Tower. Am I missing something, I'm rather frustrated!

In his workshop there is a tank dispenser next to the only open door in the room on the other side of the filling tank you used the first time you came to Piero.

That is what I was afraid of. There is no empty tank to be found. I mean... I see the filling station part, but the "dispenser" on the other side isn't doing anything. Maybe logging back in will jiggle it. (not to get all technical)

Ha! Logging back in and it worked... maybe a momentary glitch?

IIRC upstairs in the workshop is the dispenser for the empty canisters - or is it not dispensing ?

It wasn't letting me interact, but when I reloaded the game it worked fine. So... problem solved. I am on to the last chapter.