Owners of older cars may decide to clean their own fuel tanks rather than paying a professional to do so. Gasoline is lighter than water and will float on it; as a result, you will not be able to clean your fuel tank with water alone. You can buy fuel tank cleaning products at automobile parts stores, but you could also mix muriatic acid with hot water for equally impressive results.
Ensure that your tank is empty before starting to clean it. You may wish to drive around for a while to consume whatever fuel remains.
Consult your car's manual and properly remove the fuel tank.
Fill the tank to half-full with hot water, then add about a half gallon of the muriatic acid. Proceed to fill the remainder of the tank with more hot water. Let this mixture settle in the tank for about two hours, then dispose of it responsibly; disposing of it down the sink or drain is not recommended. After you have emptied the tank, wash it out thoroughly with water, outside and in.
Apply the fuel tank cleaner as per instructions on the bottle if you are using this instead of muriatic acid. Again, after cleaning, ensure that the tank is thoroughly rinsed, inside and out, with water.
Repeat Step 3 or 4 until nothing emerges from the tank except water.
Wait for around 24 hours until you're sure the tank is completely dry, then reattach the tank correctly to your car, following your car's instruction manual.
Muriatic acid and car fuel tank cleaning products can be irritating and/or corrosive; always wear thick rubber gloves throughout the process. Perform this process outdoors to avoid inhaling dangerous fumes.