The past couple of fill ups, I've  noticed the rear of the fuel flap, the cap itself and the recess have been covered with salty  road muck. A spray with MucOff and several scrubs with a  soft paint brush and a rinse with warm water -it looked ok. But I then spot a blocked drain hole and give it a clean with some stiff mains cable. Another rinse and the water drains away faster with a good gurgle . A nice satisfying job while the sun was out .

12 hours ago, gregoir said:

The past couple of fill ups, I've  noticed the rear of the fuel flap, the cap itself and the recess have been covered with salty  road muck. A spray with MucOff and several scrubs with a  soft paint brush and a rinse with warm water -it looked ok. But I then spot a blocked drain hole and give it a clean with some stiff mains cable. Another rinse and the water drains away faster with a good gurgle . A nice satisfying job while the sun was out .

 

I noticed that the other day whilst washing the car. A blast with the pressure washer soon sorted that out