The Stanley flask was a great Christmas gift from my wife a few years back. But when I went to use it for the first time, filling it was a challenge. But then Makerbot to the rescue! This custom funnel fits perfectly and is very secure so you don't need to hold it while filling, just the flask itself.

Customized version of http://www.thingiverse.com/thing:49597

Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=49597