Which of the following is an acceptable method for cleaning an aluminum fuel tank?

Using warm water and a soft brush is an acceptable method for cleaning an aluminum fuel tank because it effectively removes contaminants without causing damage to the metal surface. Warm water can help to break down oils and other residues that may have accumulated, while the soft brush gently scrubs the interior surfaces without scratching or abrading the aluminum. This combination ensures that the tank maintains its integrity and prevents the introduction of particles that could contaminate the fuel system.

The other methods can potentially compromise the aluminum surface or introduce contaminants. For instance, using a scrubbing pad may create scratches, risking corrosion or structural weakness. Bentonite clay, while effective for some applications, is not suitable for cleaning a fuel tank and could leave residues that interfere with fuel quality. Meanwhile, dry cleaning solvent can be harsh and might not be safe for use on aluminum, as it may react adversely with the material or leave behind harmful residues. Therefore, the use of warm water and a soft brush is the most effective and safe approach for maintaining aluminum fuel tanks.