Abstract: An apparatus for a fuel tank filling and level monitoring device. The apparatus 10 provides an inexpensive and simple means of monitoring the fuel level in a tank 14 while it is being filled. A translucent cylinder 22 threaded on both ends 34, 36 is attached to the inlet 12 of the fuel tank 14. The operator 24 then inserts the nozzle 18 of the filling apparatus 20 into the end of the translucent cylinder and begins to fill the tank 14. When the tank 14 is filled to capacity the level begins to rise into the translucent cylinder 22 indicating the tank is full. The operator 24 then stops filling the tank 14, removes the nozzle 18 of the filling device 20 and applies the original cap from the fuel tank inlet to the end of the cylinder. Also disclosed are embodiments with a rigid body, a flexible body and as a component of a fuel tank.