Prepare the necessary tools, materials, and a safe workspace. Gather new seals that match the petrol tank's make and model—check the tank's specifications to ensure compatibility.

You'll need a flathead screwdriver or plastic pry tool to avoid scratching the tank, lint-free cloths, a mild cleaning solvent, and protective gear including gloves and safety glasses.

Choose a well-ventilated outdoor area away from ignition sources like heaters or smokers, as petrol vapors pose fire risks. If the tank is mounted on a vehicle, drain any remaining petrol into an approved storage container first—never work on a tank with fuel inside.

Start with accessible seals like the fuel cap seal: twist off the fuel cap and gently peel or pry the old seal from its groove using the plastic tool.

For seals around the filler neck or tank connections, you may need to loosen fasteners such as clips or bolts that hold the component in place.

Take care not to damage the tank's surface or the component's groove—avoid using sharp metallic tools that could create scratches, which might prevent the new seal from seating properly.

Once the old seal is removed, use a lint-free cloth dampened with mild solvent to clean the groove and surrounding area, wiping away any dirt, residue, or old adhesive.

Before installation, check the new seal for any defects like cracks or tears. Align the seal with the tank's groove, ensuring it fits snugly without stretching or twisting—stretching can weaken the seal and lead to leaks later.

For fuel cap seals, press the seal firmly into the cap's groove until it sits flush. For filler neck or connection seals, slide the seal into the groove first, then reattach the component to the tank, tightening fasteners gently but securely.

Avoid over-tightening, as this can deform the seal or damage the tank's mounting points, compromising the seal's effectiveness.

After installing the new seal, perform a leak test to confirm the fit. Reconnect the tank if it was removed and add a small amount of petrol to the tank.

Wipe the sealed areas with a dry lint-free cloth, then check the cloth for petrol stains after a few minutes. If no stains appear, add more petrol gradually and continue monitoring for leaks.

For fuel cap seals, close the cap tightly and gently shake the tank if safe to do so to check for vapor or fuel escape.

Dispose of old seals and cleaning rags according to local regulations—petrol-contaminated materials are hazardous waste.