First, is your gasoline actually bad?
Gasoline degrades by oxidation over time, and ethanol-blended fuel (most pump gas in the U.S., usually E10) degrades faster because ethanol attracts water. As a general rule of thumb from the fuel industry, untreated gasoline stays usable for roughly three to six months, while a fuel stabilizer such as STA-BIL is marketed to keep it fresh for up to about two years. These are manufacturer and industry figures, not a government standard, so treat them as guidance rather than a hard expiry date.
If the fuel still looks clear and smells like gasoline, it is often still usable — especially if diluted with fresh fuel. Gas that has turned darker, smells sour or like varnish, or has water or sediment in it is more likely to cause hard starting and is a candidate for disposal.
The right way: a household hazardous waste (HHW) site
The U.S. EPA classifies leftover products that can catch fire — gasoline very much included — as household hazardous waste, and the correct route is your local HHW program. As New York's environmental agency (DEC) puts it plainly: never pour gasoline into storm drains, septic systems, or onto the ground, and never put it in household garbage or recycling.
Contact your town or county government or solid-waste district to find a permanent HHW facility or a periodic collection event. Most county HHW programs accept gasoline free for residents, though some limit quantities or require an appointment. One practical tip from county programs: staff usually won't pour the gas off at the site, so plan to leave your gas can behind at the drop-off.
Can you just reuse old gas instead?
Often, yes. According to NY DEC guidance, old but uncontaminated gasoline can be reconditioned — filter out any particles, and if there's a little water, a fuel dryer can help — then blended with fresh gasoline at roughly a 1:5 ratio (one part old to five parts new) and burned in equipment you don't mind testing it in, like a lawnmower. Check your owner's manual first, and do this work outdoors away from any flame or spark.
The exception: gasoline that has been contaminated with other fluids such as brake fluid or antifreeze cannot be reconditioned or reused. That's hazardous waste and has to be disposed of at an HHW site. Never mix gasoline with other automotive products.
What NOT to do
Don't let it evaporate. Gasoline vapor is heavier than air and collects in low spots, where any spark can ignite it — and the vapor releases benzene, a known carcinogen. Deliberately evaporating usable gas is both a fire hazard and an air-quality hazard.
Don't assume an auto-parts store will take it. Chains like AutoZone accept used motor oil and batteries for free recycling, but that's not the same as gasoline — and motor oil mixed with gas is rejected as contaminated. Route gasoline to HHW instead.
Don't pour it out anywhere — storm drain, yard, toilet, or trash. A single improper dump can contaminate soil and groundwater.
Storing and transporting it safely
Keep gasoline in its original fuel container or a UL-approved metal safety can (by convention, gasoline cans are red). An approved safety can holds no more than five gallons and has a spring-closing lid and a spout. Store it away from heat and out of reach of children and pets.
When you drive it to the HHW site, keep the container upright and secured — in the trunk or truck bed, away from passengers — with the fill and vent openings closed tight.