The easier rules are conditional, and the condition is segregation
Used oil managed for recycling, and lead-acid batteries, lamps and aerosol cans managed as universal waste, all carry reduced requirements compared with full hazardous waste: simpler storage, longer holding, less paperwork. Every one of those regimes is conditional on the material being kept in its own stream. Pour solvent into the used oil tank and you have mixed a hazardous waste with used oil, which changes what the tank contains and how it must be handled. Put batteries into a hazardous waste drum and they stop being universal waste. The economics of an automotive site are therefore decided in the shop layout and the labeling, not in the disposal contract — a site with the right number of clearly marked containers pays a fraction of what a tidy-looking site with one general drum pays.