No 2 is your feed from the tank
No 3 feeds the filtered fuel to the engine,
No 1 is a link back to the tank for heated excess fuel,
No 4 is also part of this system
have you seen the speed a fuel pump pumps fuel?The best way would be to remove the fuel filter and run a feed to the fuel pump. This would then quirt the fuel out so you can catch it in a washing up bowl or something similar.
Yes they have, give the pump 12v and empty it from the bottom.
Another way is if you get hold of a pella pump, you can lift the back seat and remove the cover to the diesel pump and suck the lot out from there.