That's ancient gas..
I've never had so much to dump, but some ancient motors like my honda z50 will run on 5 year old gas.
Other than that, you can light it in an
oil drum, or find a safe spot to pour it in a drum and let it evaporate.
If you have really cheap friends, some might take a gallon or two mixed into their tank if their car is old and not picky. Over here that's a $12 gift (2 gallons)