Motor oil & transmission fluid
Since motor oil needs to be routinely replaced, if you change your car’s oil yourself, you’ll have to deal with the ‘waste oil’ every now and then. Do not dump it down the drain—it’s actually illegal to discard it that way. When oil mixes with groundwater, contaminates can prevent sunlight and oxygen from permeating the water (and this affects aquatic life). Instead, return used motor oil or transmission fluid to any service station—they’ll take it off your hands and dispose of it properly.