Used a high pressure attachment on the hose and blasted the one we had – wasn't a large nest though, but could stand far enough back not to be in their sting zone. It knocked the nest off, they rebuilt, I did it again and they moved on.
Almost humane!

Oh, and the wasps are Aussie ones so think more hornet sized (and probably lethal).
…

Actually, I don't like killing wasps, the ones around our house make little cocoons and stuff a spider in them as food for their young. Though I think this is probably too big to box up:

More on the mud nest wasps here. Australia is ace.