Source: https://www.dailymail.co.uk/femail/article-9108379/Brainteaser-leaves-puzzlers-stumped-work-flute-filled-first.html
#Modified
Solution: The correct order they will fill is 2, 4, 1 and then 3.
source http://www.nairaland.com/6345600/brain-teaser-which-glass-filled
