Old fuel disposal or use ?

Add a few gallons at a time to a tank with several gallons of good gas. It'll burn. I used to do this on my carbureted, no cat con step van engine. I did it often, as I used to run a mobile small engine biz, and the number one repair was cleaning out old gas, which I then had to get rid of.
I can't speak to something that has smog stuff and/or a computer.