Preventive use Fill the fuel filter up with Diesel Purge when doing filter replacement, put the rest in tank. Remedial use Unclip the fuel pipe and immerse the end in the Diesel Purge. Close the fuel return pipe or feed that into the Diesel Purge. Start the engine and allow the engine to run at different speeds with the Diesel Purge unmixed. After the cleaning process, assemble the vehicle's system. In extreme cases, repeat the cleaning procedure if necessary.