What have you stolen from and how?

[Jack Mann]

Water Jug:

Or you could fill them both halfway, and then pour the 1.5 gallons in the 3 jug into the 2.5 gallons in the 5 jug. 1.5+2.5=4

The problem is doing it exactly. That requires a degree of eyeballing. The shape of the jugs could make this very difficult.