Start by preparing the tank for cleaning: first, fully empty all remaining fuel, either by using it in equipment or transferring it to a separate, approved storage container. Ensure the tank is in a well-ventilated area to prevent the buildup of flammable fumes, and wear protective gear such as gloves and safety glasses to shield against fuel residues or cleaning agents.

Remove any loose debris or sediment from the tank's interior. This can be done by gently wiping the inner surfaces with a soft, lint-free cloth or using a long-handled brush designed for tank cleaning—avoid using abrasive tools that could scratch the tank's material, as scratches may lead to corrosion or leakage over time.

For stubborn residues, such as dried fuel deposits or sludge, mix a mild, fuel-compatible cleaning solution (such as a specialized tank cleaner or a diluted detergent that is safe for the tank's material) with warm water. Pour this solution into the tank, then seal the opening and gently agitate the tank to ensure the solution reaches all inner surfaces. Let the solution sit for a period to break down residues, then drain it completely.

After draining the cleaning solution, rinse the tank thoroughly with clean water to remove any remaining cleaner or dissolved residues. Repeat the rinsing process until the water runs clear, as leftover cleaning agents can contaminate future fuel supplies. Once rinsed, dry the tank's interior and exterior completely—use a clean cloth to wipe down inner surfaces, and leave the tank in a well-ventilated area with the opening uncovered to allow any remaining moisture to evaporate.

Inspect the tank for any signs of damage, such as cracks, scratches, or worn seals, before refueling. Check that all safety components, like pressure relief valves or sealed caps, are functioning properly and free from debris. This post-cleaning inspection ensures the tank remains safe and effective for future use.