I frequently change the oil in my own vehicle.
However, I have a lot of waste oil I am storing that has built up over time. How can I use this waste oil for my personal benefit?
If you have some wood outside that needs some protection, old motor oil is cheap alternative for store bought wood preservers. I am not any kind of wood working professional so check other sources about this.
I have a small wooden fence protected with old motor oil in my backyard and it holds great.
Here is a video of someone using this technique.
It is possible you don't need to change the engine oil as often. For some reason, many Americans think they need to change the oil every 3000 miles when the manufacturer's recommendation is more like 15000 miles. So the first step to reducing waste is to check what the manufacturer recommends.
Many modern cars have a function in the engine management system that tracks the state of the oil and indicates when you need to change it. Depending on your driving habits, this can extend the life of the oil even further.
I don't recommend reusing the oil in another vehicle. The whole reason to replace the oil is that oil degrades over time. It becomes contaminated with not just metal particles (which you could filter out) but you can also get water, petrol and/or coolant in the oil.
Although a car has a lot of engine oil and it's not possible to use it all, some amount of it can prove to be useful. You can use the old oil for oiling/lubricating household machinery. For example, it can be used in sewing machine, in fan motor of room cooler and room heater. By putting oil on jammed screw and nut bolts, we can easily open them.
Apart from this if you have an old vehicle in which you do not want to spend a lot of money buying new engine oil, just filter this old engine oil using a fine cloth and use it.
Use it to paint the underside of your car to prevent rust. Offer it to neighbors to do the same. Start a little business offering to paint & somewhat rustproof the underside of cars. Finally, if nothing else uses it up, bring it to a recycling center.