Thank you both for responding with excellent suggestions. I will check on them all.
Ted might be right about air blockage in the lines. When I filled the tank for the first time, literally not a drop of gas flowed into the filter for hours. If it needed a suck from the engines like comfortableshoes suggested, the gas would have at least drip into the filter's neck and sat atop the paper element.
I don't think there are any air leaks and definitely no fuel leaks. All fuel connections were so tight I had to use thread sealant as a lube to push on the fuel hoses. All three tanks are vented thru their caps. The teardrop tank is vented through the keyhole in the locking gas cap. I gave it the "suck/blow" test.
At least I can use the teardrop tank as a storage tank and siphon to both engines' tanks until I solve this problem.