Chevrolet GMC 2002 Owner's Manual Supplement page 36

To drain water in 3500HD models:
1. Stop and park the vehicle in a safe place.
Turn off the engine and apply the parking brake.
2. Remove the fuel cap.
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3. Place a fuel resistant container under the filter drain
hose. The filter drain hose is located on the front of
the engine and is connected to the water drain valve.
See "Engine Compartment Overview" in the Index
for more information on location.
3500HD Models
4. With the engine off, open the water drain valve
two to three turns. The valve is located to the left
of the engine oil fill cap, when standing in front of
the vehicle.
5. Start the engine and allow it to idle until clear fuel
is observed. If no liquid comes out, your vehicle
needs service.
6. Stop the engine and close the water drain valve.
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7. Remove the fuel resistant container and properly
dispose of the contaminated fuel. To find out how
to properly dispose of contaminated diesel fuel,
see "What to Do with Used Oil" in the "Engine Oil
(Diesel Engines)" part, later in this section.
8. Install the fuel cap.
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