Flyboy's 'lair' is located to the south of the area, up a rather large oil rig. It's easy to spot thanks to the large 'FLYBOY' graffiti scrawled in red above.
To get up to Flyboy you will need to deal with a range of basic bruisers, bikers, psychos and enforcers. Bring a flame weapon with you and you'll cut a swathe through them without much difficulty. Work your way up the rig when you can, watching out for mre enemies as you scale the construction.
Boss â€“ Piston's Blimp
Yup, not Flyboy. This blimp is a huge target, so start pumping bullets/rockets/marmots into it with extreme prejudice. The Blimp's key attacks see it rain missiles upon you, so try and keep a large building in between yourself and the blimp that you can use to avoid/soak up the onslaught. Otherwise just keep peppering the vehicle with attacks to bring it down.
Head back to Moxxi. Almost time for the final showdown...