How to clean opel astra 1.8n 1999 fuel tank?

To clean the fuel tank of a 1999 Opel Astra 1.8N, first ensure the vehicle is safely lifted and the fuel is drained completely. Remove the fuel tank from the vehicle, then rinse it with a mixture of water and a suitable fuel tank cleaner, using a brush to remove any deposits or sludge. After thorough cleaning, rinse with clean water and let it dry completely before reinstalling the tank. Ensure all seals and connections are secure before refilling with fuel.