Turn off the lawnmower and set the parking brake, if applicable. Let the engine cool before attempting to remove the fuel bowl or you may be burned.
Take the cap off the lawnmower's gas tank and insert the hose of a hand siphon into the tank. Place a plastic gas container near the mower.
Squeeze the hand siphon several times to empty the lawnmower's gas tank. Try to siphon out all the fuel from the tank as it will drip when you remove the fuel bowl. Remove the siphon.
Locate the fuel bowl under the carburetor on the engine. Grasp the ferrule or nut holding the fuel bowl in place with pliers. Turn the pliers counterclockwise until the ferrule or nut comes loose. The fuel bowl will now dangle from the fuel lines.
Grasp the fuel lines and bowl with your hands and pull firmly in a downward motion to free the fuel bowl from the lines. A small amount of gas will drip out of the lines as well as the fuel bowl. Take the O-ring out of the end of the fuel bowl and set it aside. You can now install a replacement.