NewPing Library: HC-SR04, SRF05, SRF06, DYP-ME007, Parallax PING))) - v1.7

I would also suggest a float because then the electronics can be placed outside the tank with only the float on the inside. Putting electronics inside fuel vapor doesn't sound like a good ideal. Actually, it sounds like a very bad idea. A short could result in a spark which results in a very bad day.

Tim