Tank sender unit and pump?

Just had a look inside of my fuel tank through the sender unit under the rear seat to check for rust and dirt and it has 2 pipes going to it and also what looks like a small pump of some kind? I had to take off the two pipes to remove it all but no fuel came out. What is it and what does it do. I didn't see anything in my Bentley manual about it. it buzzes as the engine idles over. thanks

its the lift pump. it pumps fuel to a smaller tank that feeds the main pump.

Thanks for the quick reply. Ok great that makes sense.