I had a gallon bottle that I used. I only filled it completely maybe twice in seven years. I’d pull over on the shoulder in the country and pour it out the passenger window. Give it a good rinse every few days and a thorough washing every month or so and it wouldn’t even stink.
Even for the people that use small bottles and throw them out, they can save them long enough to throw them away at a truck stop. There’s no excuse for throwing your full piss bottles and other trash on the side of the road.