Do some cars have siphon blocks The siphon does not seem to reach the gas Is there a kind of screen or block in some cars that prevents the siphon from reaching the gas if so how do you siphon it i.e?

There is sometimes a mesh type of anti syphon filter deep down in the tank where you normally couldn't reach it. You might damage the filling pipe and cause leaking gas if you try to remove it or break it. These are put there for obvious reasons. Some older cars eg 1970s can be drained from underneath by undoing the plug if you are wrecking your vehicle and want to prevent a fire hazard