Place the Stihl chainsaw on a flat surface and set a gas can next to the fuel tank of the chainsaw. Twist the cap on the fuel tank counterclockwise and remove it from the chainsaw. Insert a hand siphon into the tank and the opposite end into the gas can. Siphon the fuel out of the chainsaw into the gas can.
Cut the bottom off a metal clothes hanger, using wire cutters. Bend a hook on one end of the hanger, using needle-nose pliers.
Insert the hook end into the fuel tank and hook the fuel ine in the bottom of the tank. Pull the fuel line up until you can grab it with your fingers. Pull the fuel line until the end with the fuel filter is out of the tank.
Hold the end of the fuel line in one hand and pull off the fuel filter with your free hand. Insert the nipple of the new fuel filter into the end of the line, until the end of the line is flush against the filter.
Push the filter and fuel line back into the fuel tank. Shake the chainsaw until the fuel line is flat on the bottom of the fuel tank. Fill the tank with gas and twist the cap back onto the tank.