How to Clean a Gasoline Tank. Whether you drive a car, truck or motorcycle, if you really on gas to get around, your gasoline tank is going to get dirty, on the inside as well as the outside. Getting rid of rust isn't the only necessary maintenance for a gas tank. Remove and clean your tank about once a year.
Make sure your vehicle is as empty of gas as you can before removing the tank. Drive the vehicle until the tank is nearly empty, then let it sit and idle until it stops. Remove the gas tank from your vehicle according to the vehicle manual. Once it's off, wipe out any remaining gas. If you see any holes that need to be welded, now's the time to do it.
Wash the tank with dish soap and water (you can also use laundry detergent). Use a stiff brush to remove any tough grime. Let the water drain out, then seal the bottom of the tank with duct tape.
Fill the tank with a fuel tank cleaner that can be found at most auto stores. Check the instructions on the cleaner. Some need to be diluted with water. You can also use a muriatic acid/water mixture, though the acid is corrosive and must be used sparingly. Again, check the instructions on the acid before filling your tank. Depending on the size of your tank and its condition, you might use as much as 2 gallons of muriatic acid.
Let the tank sit for at least 12 hours to break up any hardened material. Drain it and wash it again with soap and water. Towel dry the entire tank, inside and out. Then let it sit in a dry location for at least 24 hours. The tank must be completely dry before you put it back on the vehicle.