Bus Maintenance?

Refilling bus tank
Refilling bus tank

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!