Bear in mind that gasoline is a witches' brew of about 60 fractions and additives designed for a working life of 60-90 days. There's stuff like heptane and butane that just boils out as it sits there. So, if your gasoline is older than that?
Pump, pour, etc the gasoline off the top and when it gts near the contamination at the bottom, transfer it to another taller thinner container and let it decant again, then repeat from the top. When you get down to "that's enough" the rest can usually be dumped at any gasoline station in the waste
fuel/oil.
I'd use the salvaged gasoline (with octane booster) mixed into new
fuel--not straight. Mixed 1:10 or 1:4 it should burn just fine, anything stronger than that I'd only burn it in a 2-stroke.