I have heard the proper technique involves a gallon jug afixed front and center to the driver seat on the floor and a funnel with a flexible neck (surgical tubing) and proper "contact" seal with the funnel opening to make a deposit. My brother in law runs a small fleet. He does the maintenance on the trucks on the weekends and hates emptying the "thunder jugs" as they call them. They don't discard them on the road, they get dumped down a toilet in the shop.
Hey!...time is money...I ain't got time to stop and pee!
In the old days they had the "chauffeur's leg" -- a similar device to what you describe. The chauffeur was expected to hold it so long as MiLady didn't need to stop. The "leg" offered en-route relief.
We're talking Classic Era, pre-WWII here.