Flush it down the toilet.................JUST KIDDING!!!!!!!! Most towns have amnesty days where you can turn in old gas, oil, pesticides, etc. and there is no penalty on you for having them. If the gas is only a year or so old you could do the mixing routine with new gas, but for $ 20 worth of gas it may not be worth the damage it might do to your engine, such as plugging the carb or injectors. Gas today gets real bad real fast.

Don