It is a sad fact that steel petrol tanks will rust due to the exclusive use of unleaded fuels nowadays. Even tanks which are kept full at all times, and tanks fuelled by oil mixes can be expected to corrode over time. This is an easy, effective and environmentally friendly way to get rid of the rust.
Drain the petrol tank completely, disposing of the waste properly. Rinse the tank well, and drain it again. Allow it to dry thoroughly.
Empty the package of aquarium gravel into the petrol tank.
Cover all openings of the tank with pieces of thick corrugated cardboard. Secure the cardboard by sealing it into place with duct tape.
Wrap the petrol tank completely with the blanket or quilt. Place the parcel into the pillow case to ensure that it doesn't come unwrapped. This will protect the tank from being damaged by the barrel of the clothes dryer, and vice versa.
Adjust the dryer's heat setting to "Off." This is very important.
Place the bundled petrol tank into the dryer, and tumble it for several hours.
Remove the petrol tank from the dryer and unwrap it. Detach and discard the cardboard and duct tape. Shake the rust particles and gravel into a trash receptacle. The action of the gravel inside the constantly moving tank will have loosened all the corrosion. Rinse and dry the tank thoroughly.