The ventilation ducts in large buildings are roughly 1m^2 in cross-sectional area, branching out to ducts that are roughly.1m^2 in cross-sectional area.
A python is 6 meters long and has a cross-sectional area of .015m^2.
Assuming the aspect ratio of the snake body stays roughly constant, a basilisk is 15 meters long, and would have a cross-sectional area of .094m^2. Barely enough to through ventilation ducts.
The ventilation ducts in large buildings are roughly 1m^2 in cross-sectional area, branching out to ducts that are roughly.1m^2 in cross-sectional area.
A python is 6 meters long and has a cross-sectional area of .015m^2. Assuming the aspect ratio of the snake body stays roughly constant, a basilisk is 15 meters long, and would have a cross-sectional area of .094m^2. Barely enough to through ventilation ducts.
I think basiliks are a little thicker than pythons (from the second movie) and much longer than 15 m (from awesomeness).