The feeding hatches on the large tunnel seem to defy logic as to why the water does not pour out. br I knew this aquarium had used a principal I aired on "YouTube" but assumed the feeding hatches were under vacuum.In fact it is a very clever optical illusion even though the large glass tunnel is under vacuum.The hatches are exactly on the "water-line" of the reservoir tanks that feed the tunnel.The small hemispherical bowl keeps a level of water to seal the inlet holes from outside air pressure while the volume above is under vacuum.