Diesel fuel problems....

[ninaandphil]

Hi all, had a new fuel tank pump fitted during week, which has turned out to be a bit 'iffy'.... i.e not always working! Bigger problem though is that when pumps are turned off, all fuel drains back into the fuel tank, making starting a nightmare, had to clear air from injectors to get it started just now.
Does anyone know why fuel is draining back into tank... you can hear it rushing back as soon as engine turned off, I'm sure the whole fuel system shouldn't empty??
Any help pointers / advice... ZT diesel, 2003, twin pump.
Both pumps working at present, just the lack of fuel once you turn off engine... :-(