I learned the OP's lesson, years ago, when I was a student pilot.
I was on a ladder checking a fuel level in a wing tank of a flight schools high wing aircraft. I Managed to let a fuel level measuring device slip out of my fingers, and drop into the wing tank.
Removing the tank would have meant draining a large amount of fuel, and disassembling part of the wing. Which would have been somewhat expensive. :irked:
After considerable maneuvering, I was eventually able to get a "grabber tool" to hold on to one end of the hollow tube, long enough to get it out.