Jonas fills a bathtub with water
Here's a description of the contestant's attempt. Someone's probably working on collecting some images to illustrate it.
Jonas actually discovers the trick to the box, and uses his preparation time to tape a curved pipe to where the water will eventually come out. The problem is that the pipe length is too small before it curves, so when combined with the water pressure, most of the water just flows backwards out of the pipe instead of into the bucket Jonas is holding to collect the water. Jonas moves 5.35 litres and comes fourth.
(Written by Jenny R and proofread by Karl Craven)