When changing the oil in your car, motorcycle, outboard motor, or any kind of engine, it is important that the used oil is disposed of properly. The oil from a single oil change can ruin the taste and quality of a million gallons of drinking water; enough to supply more than fifty people for a year. Whenever changing oil, make sure to drain the used oil into a container. There are special containers designed for oil changes that can make this process easier. Once you have changed the oil several times, you can empty the container for free at several locations. Hardware stores commonly accept used oil, as do boatyards, and automobile repair shops.
For bulk oil, you may have to call around looking for a recycling plant or other location capable of accepting large quantities of used oil.