To drain gas from a lawn mower, first run the engine until it stalls to use up fuel in the carburetor, or let the engine cool completely. Place a drain pan under the fuel tank, then use a siphon pump to remove the gasoline, or disconnect the fuel line if accessible. Dispose of the old gasoline properly at a local hazardous waste facility—never pour it down drains or onto the ground.
Why You Should Drain the Gas
Draining the gas from your lawn mower is an essential maintenance task that protects both the engine and your investment. Gasoline begins to degrade as soon as it is exposed to air, and modern fuel blends containing ethanol can break down even faster. Over time, the volatile compounds in gasoline evaporate, leaving behind a sticky, varnish-like residue that can clog the tiny jets and passages in the carburetor. This residue is one of the most common causes of hard starting, rough idling, and poor performance in small engines.
Stale fuel can also cause more serious problems. The ethanol in many gasoline blends attracts moisture from the air, which can lead to phase separation—a condition where the ethanol and water separate from the gasoline and settle at the bottom of the fuel tank. This watery mixture can be drawn into the engine, causing corrosion, rust, and damage to internal components. In addition, old fuel can leave deposits on the spark plug and in the fuel lines, further degrading performance.
Draining the gas is particularly important before long-term storage, such as over the winter months. A fuel system left full of stale gasoline will almost certainly cause problems when you try to start the mower in the spring. By draining the tank and running the engine until it stalls, you also empty the carburetor and fuel lines, preventing the formation of deposits in these critical components. This simple step can save you significant time and money in repairs and make spring start-up effortless.
Tools and Safety Preparation
Before you begin draining the gas, gather the necessary tools and take important safety precautions. The primary tool you will need is a siphon pump, which can be a manual hand pump or a simple siphon hose. A drain pan or approved fuel container is essential for catching the gasoline as it flows out. You may also need a wrench or pliers if you plan to disconnect the fuel line, and a funnel can help when transferring fuel to a disposal container. Always use containers that are approved for fuel storage and never use glass containers, which can break and cause spills.
Safety is paramount when working with gasoline, which is highly flammable. Always perform the draining process outdoors in a well-ventilated area, away from any sources of ignition such as pilot lights, sparks, or open flames. Never smoke while working with fuel. Allow the engine to cool completely before you begin, as a hot engine and exhaust system can ignite gasoline vapors. It is also wise to wear safety glasses and gloves to protect against splashes, and to keep a fire extinguisher or a bucket of sand nearby as a precaution.
Before starting, check the mower’s fuel system for any obvious leaks or damage. If you notice fuel leaking from the tank, lines, or carburetor, address the issue before attempting to drain the gas. Place the drain pan or fuel container on a stable, level surface beneath the fuel tank, and position it to catch any spills. If you are working on a riding mower, you may need to raise the mower deck or remove a panel to access the fuel tank, and you should always ensure the mower is on a flat surface with the parking brake engaged.
Step-by-Step Draining Methods
There are two primary methods for draining gas from a lawn mower: using a siphon pump or running the engine until it stalls. The method you choose will depend on the amount of fuel in the tank, the accessibility of the fuel system, and your personal preference. For a tank that is full or nearly full, a siphon pump is the most efficient and cleanest method. Insert the siphon hose into the fuel tank, ensuring it reaches the bottom, and pump until the fuel begins to flow into your drain pan or container. Be patient, as siphoning can take several minutes for a full tank.
If the tank is low on fuel, or if you want to ensure the carburetor and fuel lines are completely empty, running the mower until it stalls is an effective method. Start the engine and let it run at a normal operating speed until it sputters and dies from lack of fuel. This process uses up the fuel in the tank, the fuel lines, and the carburetor bowl. After the engine stalls, attempt to restart it a few times to draw out any remaining fuel from the lines. Once the engine will no longer start, the fuel system is effectively empty, and you can then drain any residual fuel from the tank using a siphon if needed.
For mowers with an accessible fuel line, you can also drain the gas by disconnecting the fuel line from the carburetor or the fuel filter. Place your drain pan beneath the connection point, then loosen the clamp and carefully pull the line free. Fuel will flow out by gravity, so be prepared to catch it all. This method can be messy and may require you to replace the fuel line clamp, but it is the most thorough way to empty the system. Regardless of the method you use, be sure to dispose of the drained fuel properly, as described in the next section.
Proper Gasoline Disposal
Proper disposal of old gasoline is both a legal and environmental responsibility. Never pour gasoline down drains, toilets, sewers, or onto the ground, as it can contaminate groundwater, harm wildlife, and create fire hazards. Gasoline should never be mixed with regular household trash or placed in curbside recycling bins. Instead, old fuel should be taken to a designated hazardous waste collection facility or event, where it can be handled and disposed of safely.
To find a disposal location, check with your local municipality, county government, or waste management authority. Many communities hold periodic household hazardous waste collection days, and some transfer stations accept fuel year-round. You can also contact local auto parts stores, recycling centers, or service stations, as some may accept old fuel or be able to direct you to a facility that does. When transporting the fuel, use an approved, sealed fuel container and place it securely in your vehicle, away from passengers and heat sources.
If you have only a small amount of old gasoline, you may have another option. Some experts suggest mixing a small quantity of old fuel with fresh fuel in a vehicle or other engine that is used regularly, in a ratio of no more than one part old fuel to nine parts fresh fuel. This can safely burn off the old gasoline without harming the engine. However, this method is only appropriate for small amounts and should not be used if the fuel is contaminated with water, debris, or other substances. When in doubt, always choose the safer option of taking the fuel to a hazardous waste facility. After draining and disposing of the fuel, you can also consider adding a fuel stabilizer to fresh gasoline before storage to prevent future degradation and extend the life of your fuel.
