Fuel tank plumbing

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I've been doing some planning and reading about fuel system plumbing. I have an upper wing center section tank and was thinking about setting it up to drain directly into the main tank. My question is where on the main tank do you attach the drain from the upper tank? Is it acceptable to have a tee on the bottom of the main tank (fuel feed) and tie the line from the upper tank into that tee or does the top tank drain need to enter at a higher point on the tank?

My thinking with it set up this way is that if there was 10 gallons of fuel left in the main tank and there was only, say, eight gallons in the upper tank, then there wouldn't be enough weight of fuel in the upper tank to overcome the greater weight of fuel in the main tank and it would not gravity feed into the main. Am I thinking correct here guys??

I don't have an inlet midpoint on the tank but could have one insalled if necessary.

 

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