What is the standard procedure for cleaning a polyurethane foam air filter element used in most small underbone motorcycles?

1. Wash with kerosene or a high-flash point solvent, squeeze out the excess, dry it, and then saturate with clean engine oil and squeeze out excess oil.
2. Blow with high-pressure compressed air from the inside out and wipe the exterior surface with a dry cloth.
3. Wash with gasoline, wring it out tightly, and install it immediately to allow the fuel to clean the carburetor.
4. Soak in hot soapy water, wring it out to dry, and install it dry without applying any oil.