This is a replacement gas cap for a typical 2.5 gallon 1 gallon and 5 gallon can often found at Lowes or Home Depot and fits on the fill tube. It is easily lost so I had to make new ones.

Gasoline may or may not agree with your particular plastic but unless flooded with gasoline for long periods ABS seems to do just fine. I don't print PLA so I don't know and I also don't know about other fuels such as diesel. But this is a useful part. It can save an older can which might have to be thrown out for loss of its cap.