How to Drain a Lawn Mower Gas Tank

Draining the old gasoline from your lawn mower at the end of the summer is an important component of its annual maintenance. Gas left to sit in the tank for more than two months may coagulate and produce a film on the inside of the tank and fuel line. Condensation also develops over time in a partially filled tank, producing moisture that can make starting the mower more difficult. When emptying the tank, important points to consider include removing as much gas as possible and putting it into a suitable receptacle, avoiding or catching spills that can damage some surfaces or seep into the groundwater, and keeping the gas away from heat sources.

High angle view of lawnmower on grass
credit: Jupiterimages/ Images
Even if you run the mower until the gas tank is dry, some fuel may remain in the carburetor bowl.

Step 1

Allow the mower to cool completely if you have just used it.

Step 2

Spread the tarp or other protective material over the work area, and position the mower in the center.

Step 3

Remove the gas cap from the top of the tank, wipe out the inside with a rag and set it aside on the tarp.

Step 4

Place the intake tube of the fuel siphon into the gas tank and the outlet end into a large metal receptacle.

Step 5

Squeeze the bulb on the siphon until you see the gas coming up the intake tube; be sure it is moving freely through the exit tube. Hold the exit tube far enough down in the receptacle to avoid splashing gas onto yourself or surrounding surfaces.

Step 6

Keep siphoning until you are sure you've gotten as much of the gas out as possible.

Step 7

Use a rag to wipe around the rim of the gas tank opening and replace the gas cap. Start the mower and allow it to run dry or until it stops on its own.

Step 8

Locate the carburetor bowl on the engine, which is a small metal cylinder, and then look for the drainage bolt, which will be on one edge under the carburetor. Place a small can under it and remove the bolt to allow the gas to drain. Wipe the bolt with a rag and replace it when the carburetor is empty.

Step 9

Drain the gas from a removable carburetor by holding a small can underneath it, removing the single bolt and pouring the gas into the container. Wipe the carburetor out with a rag and reattach it to the engine.

Step 10

Wipe gas spills from the mower itself and from the tarp and properly dispose of used rags. Sprinkle cat litter over spills that may occur on unprotected surfaces and dispose of it properly once it has absorbed most of the gas.