We received these good sketches from Christian and Kodai from the Munich International School, though I don't think the graphs should have ever become horizontal.
 
It is also worth noting that the graphs didn't always take into account the varying widths of some of the containers - e.g. when the water reaches the narrow top of the volumetric flask, how will the height of the water level be affected by an increase in the volume of water?
 
We also received good sketches from Priya, Stephanie and Aishwarya, also from the Munich International School.