Unfortunately its an either or, either it behaves like a water trough or it behaves like a water container (barrels, tubs, pitchers). We thought more choice is better, so you can have an empty and a full version. You should be able to load it up with water like the other water containers.Might want to mention that the bar piece has to be in your pack to be able to pour water into it, other wise it says "Locked down resources cannot be used!"
Any way to make the sink a SOURCE of water, like the water troughs when filled? I think many people would prefer to use these for cooking instead of having a giant ugly water trough in their kitchen!
I've always though the water troughs make nice dish tubs hehe.