It is a series of baffles in the pipe, yes. If you misfuel the easiest way to empty it is to get underneath, disconnect the fuel line and pump it out with the fuel pump. On modern diesel cars you have to flush everything out anywa y because petrol can damage some components in the injection system.Is it a grill at the bottom of the filler pipe to stop a syphon getting far into the tank? Raises an interesting question about how repairers extract fuel from a misfueled car ( petrol instead of diesel etc)