Fuel seems to drain out of the line?

[Jerblazer72]

Hi everyone,
I have finished (mostly) the frame off restoration of my 72 GMC and abm a bit perplexed with the fuel getting to the carb. Here is the set up: Blazer tank relocated to the underside of the truck bed. Filler door modififcation to be behind the rear marker light. Vent line attached and run to above the filler so that fuel will go into the tank easily. Truck was set up at the dealer with auxillary tanks. Not back in yet, but using the original tank selector switch (mechanical). Edelbrick mechanical fuel pump, new flexible fuel line from pump to the carb. The truck runs fine once I crank on it for 10 seconds till the fuel gets to the carb. If it sits more than a day its at least 10 seconds of cranking on it till it gets fuel up there to run. Once its there it runs no problems. What do I need to do to prevent the fuel from draining out of the line when it sits? Thanks.