Saw this at a rest stop along I-90 during the Semiannual Migration of the College Students…
He’s pouring water into a small funnel with a large paper cup, which explains all the spillage. I couldn’t hoist that 5 gallon bucket over my head, much less pour its contents into the tiny opening, so what he’s doing has a certain internal logic, but …
I think he’s refilling the toilet flush tank and, if so, I hope the bus designers made the drain tank much larger than the flush tank!
The Smell of Molten Projects in the Morning 
Ratios and a lot of moving parts…
http://en.wikipedia.org/wiki/Tender_%28rail%29#Water_supply
I remember my surprise when I discovered that the “coal tender” behind a steam locomotive was mostly a water tank. Either they didn’t mention that in all my childhood books or I was asleep at the switch… [grin]