I bot a one-off sailing cat with 2 44-hp Pentas and flexible Nauta fuel tanks. Tanks are old and seeping, so am ordering replacement tanks. My boat is in Mexico and I cannot inspect the system. They offer drawing nipples with 1/4, 1/2 or 5/8 inch barbs. I have no idea what size to order, but would guess the 1/2". Would anyone be able to offer a recommendation?