It seems like the barrel you bought had previously contained a product that likely contained Sodium Lauryl Ether Sulfate (SLES), a common surfactant used in various cleaning and personal care products due to its foaming properties. If you want to clean the barrel effectively, you can try the following steps:
Safety first: Before starting the cleaning process, ensure you're in a well-ventilated area and wear appropriate safety gear, such as gloves and eye protection, as some cleaning agents can be harsh on the skin and eyes.
Remove any debris: First, make sure the barrel is free of any large debris or residue. Rinse it with water and drain any excess liquid.
Use hot water and detergent: Fill the barrel with hot water and add a strong detergent. Allow it to soak for a few hours or overnight. The hot water and detergent should help break down the SLES residue.
Scrub with a brush: After soaking, use a scrubbing brush or sponge to agitate the inside of the barrel. Focus on areas with SLES residue, applying more pressure if necessary.
Add vinegar or citric acid solution: Vinegar or a solution of citric acid and water can help neutralize and dissolve any remaining SLES. Mix 1 part vinegar or citric acid with 5 parts water and pour it into the barrel. Allow it to sit for a few hours.
Rinse thoroughly: Empty the barrel and rinse it thoroughly with water several times to remove all traces of detergent, vinegar, or citric acid. Check for any remaining residue.
Use salt spirit (mineral spirits): If the SLES residue persists, you can try using salt spirit (mineral spirits) to break it down. Apply some salt spirit to a cloth or sponge and scrub the affected areas. Rinse thoroughly afterward.
Baking soda paste: If there are still stubborn spots of SLES, you can create a paste with baking soda and water. Apply the paste to the affected areas, let it sit for a while, and then scrub it with a brush or sponge before rinsing.
Final rinse and air dry: Rinse the barrel thoroughly one last time to ensure it's completely clean and free of any cleaning agents. Let the barrel air dry in the sun to ensure it's completely dry.
Always make sure you've rinsed the barrel thoroughly before using it for any new purpose, especially if it will come into contact with food or drink. Chemical residues can be harmful, so it's essential to clean the barrel as thoroughly as possible. If you find the cleaning process too challenging or uncertain, consider seeking professional advice or assistance.