I still say drain the tank. That will eliminate bad fuel as a variable and also get any gunk out of the tank. If the fuel is bad you'll end up chasing your tail trying to get it started and running smoothly. If there is water in the fuel you'll be able to see it settle out in the bottom of the container. I had a Mazda (back when they were good and made in Japan) and the owners manual recommended draining the fuel tank once a year. Of course I'd run it down to Empty before draining it. It was easy because it had a plug in the bottom like the oil pan.
Drain it and save yourself some headaches.
As for disposal you can:
1. Filter it and add it back to the tank a couple of gallons at a time once it's running fine.
2. Use it for cleaning parts.
3. An oil disposal place should take it.