Not all fuel in a 747 is stored in its wings - it has fuselage tanks too, and some models even store fuel in the horizontal stabilizer. These tanks typically are comprised of individual rubber bladder tanks that are contained within aluminum framed structural compartments within the wings and fuselage, between certain wing ribs, spars and the wing root area where the main wing center frame is mounted to the fuselage.
In addition to center main wing and body tanks, there are forward fuselage body and rear body tanks. Bottom line is that a 747 has more than a wing tank or two in each wing — there can be a half dozen tanks distributed around the aircraft.
There is no squeezing involved. The fuel is incompressible so it can’t be squeezed at all. They don’t squeeze the fuel in, they pump it into manifolds under the wings and it flows into the tanks. You can get 64,000 gallons of fuel into the tanks because the tanks have a volume of 64,000 gallons. The single largest tank on a 747 is the centre tank in the fuselage between the wings, but a lot of fuel is stored in the wing tanks.
Taking the 747‑400 as an example, the wings have an area of 525 m², about two‑and‑a‑half tennis courts. Converting to metric, 64,000 gallons is about 242,000 litres, requiring a volume of 242 cubic metres. Dividing this by the area of the wings, 525 m², we find that the wings would need to be on average 0.46 metres thick, about 18 inches, to have the required internal volume. Now of course, there’s other stuff in the wings besides fuel tanks, but this shows how the volume is available.
Fuel from each tank gets pumped around other tanks to maintain center of gravity inflight, and there is engine manifold cross‑feed plumbing and manifold tanks that actually feed each engine. Fuel tank monitoring and management during flight “is a thing,” and yet another critical pilot task, even when most of this transfer stuff might be automatic.