Nooooooo - I thought it was clear enough!
Fuel is lifted from the tank through the fuel filter by the injection pump, which goes on to deliver high pressure fuel to the injectors.
At anything less than full power, some fuel is rejected by the ECU and returned to the tank. The fuel return line has a regulating valve in it to keep some pressure on the engine-side and stop air creeping back from the return pipe.
The lines between pump and injector are solid metal, so anyplace you can see bubbles on the input side is before the pump. If you have bubbles there, I'm not sure
how to deal with them, having never done so myself.