Rhyme sorta intended!

I currently have two quests I'm looking at completing, one of which I've had for a very long time. These are "Magiteknical Difficulties" and "Crate Go Kaboom". Problem is, I've played and subsequently quit FFXIV twice since around the time I got the former quest or finished that part of the storyline.

Now I can't remember for the life of me how to get back into Castrum Centri. I vaguely remember something about a disguise using an Imperial helm and jacket, and something about a drainpipe. I've had a look around, but there doesn't seem to be any clues as to where exactly to go.

Knowing me, it's something absurdly simple that I've somehow overlooked. Any help would be appreciated.