Taillight Fuel Filler Hose Routing

[lkt1954]

I'm trying to route the filler hose from my tail light filler to my rear mounted tank.
I have a sniper fuel tank with the filler hole in the top lower left corner. I have both a straight filler neck for the tank and one like the picture. Both are 2" in diameter. I plan on going between the bed and the frame rail the up to the filler in the tail light.
I have thought about reducing down to a 1" filler (as that is the size of the end in the tail light. Then get a long filler hose with a 90 degree end to connect.
My concern is enough slope so all the fuel drains into the tank.

Can anyone who has plumbed a tail light filler to a rear mounted tank give me some advise?

Thanks
Larry