Cleaning your fuel oil tank is an important part of its maintenance and you should do it anytime you see sludge in it. If you know how to go about it, cleaning a fuel oil tank can be a simple and straightforward process. All you really need is the right cleaning solution, an air pump and an air hose. However, while it is not a difficult job, there are a few precautions you need to take to make sure it is done correctly and safely to protect the environment and the lifespan of your fuel oil tank.
Open the drainage valve and drain the fuel oil tank. Catch all the fluids into an appropriately sized receptacle. Remove the receptacle, replace it with another and use the water hose to spray the inside of the tank with water until it runs clear. Take the used oil to your local mechanic to have it disposed of properly.
Replace the drainage cap on the fuel oil tank and open the main filler. Fill the tank with a solution of 1 cup of trisodium phosphate (TSP) cleaning powder per 5 gal. water. Put an air hose into the tank through the main filler until it reaches the bottom of the tank. Turn on the air pump and leave it on overnight to agitate the solution (at least 12 hours). Drain the TSP solution. Since it is phosphate free, it can be poured into the toilet or down the drain. With the drainage cap removed, spray the inside of the oil fuel tank with the hose again.
Dry the tank. The most efficient way to do this is to pour a few gallons (depending on the size of the tank) of denatured alcohol into the tank at rotating angles so that it covers as much of the interior surface of the fuel oil tank as possible. This will absorb any remaining water. Blow air into the tank with the air hose until it is completely dry. Refill the tank.