Thinking he was just too lazy to take his rubbish with him, I went out & retrieved it.
Full of urine!
The van may not have been equipped with a bathroom/toilet... but there's no excuse for what he did.
So I marched back to his rig with the bottle.
He tried to intimidate me by standing less than a foot from my face (he's half-a-head taller) and said, "Yeah? What is it?"
Keeping ever-so-calm, I raised the bottle to eye level and told him, "It's people like you who give free-campers a bad name. Dispose of it properly." handed it to him and walked away.
I guess he was disappointed I didn't get agressive, and maybe a little shamed (I hope so) so walked into what little grass was alive, poured it out, then stowed the bottle in his ute. We made it obvious we were both watching him.
So keep your eyes peeled for a white Isuzu ute with an aluminium box canopy, blue twin-hull punt on a roof rack, pulling a Jayco Journey Outback pop-top. Vic rego: 1LU-7QQ, with 'Ballarat Isuzu' numberplate surrounds. (Couldn't get the van rego.)
The crazy part is, both he and his partner were very careful to remove their dusty shoes at the van door before entering!
