Carburetor loses prime after 8+ hours

I run about 6" of metal line off my carb and then I run rubber fuel line down to the pump.

My metal line has a 45* bend in it. What I do is position it's ever so slightly bent up in the air. That way even if the fuel does drain back down to the pump, it shouldn't be able to past that bend because it'll have to fight gravity. If you just run your line straight down, then there's no protection against it. This way even if I do have a problem, I'll still have that little bit of fuel sitting in the line up to that 45* bend.