Image imported from derpibooru
Original Description:

Twintails: “Alright, looks like the tanks should be mostly filled, if you want to go unhook them. Make sure the sight glass on the fill nozzle is fully filled before removing, alright? I’ll handle the truck.”
Octavia: “Sight glass fully filled, got it. Should be easy enough…”

Perhaps Twintails should’ve specified what the sight glass should be fully filled with, as Octavia discovered in removing the first of the tanks from the loading bay - while it was a solid color, that meant the hose hadn’t been flushed properly, so a dangerous amount of pressurized P-235 remained inside! And, while the gas masks are fine for dealing with low-pressure clouds, a high-pressure stream in close proximity is more than capable of overpowering the filter - especially when the surprise causes a sudden gasp.

Ah well, guess they’ll be staying the night after all…