Cheap gasoline, typically expiring.
"All she's fuckin got in er is some old radioactive horse piss"
A rare type of possibly expired diesel fuel, the origins of which are unknown. Typically found in shitty old Fords in Albertan oilfields.
Before we fire this old piece of shit up, we gotta see if she's got any Radioactive Horse Piss in her tank.
Some sort of mysterious hydrocarbon fuel that may or may not run an engine. God knows what it's made of or how old it is. Often found in the fuel tanks of broken lawnmowers and abandoned trucks.
"I don't know what's in this jerry can. Probably just some radioactive horse piss."