EDIT: for clarification: There is only so much space between the front of my head and my brain. How does so much snot fit in there? Is it generated continuously so that there is always more available? Does it come from the lungs, and if so, what is the process of transport to my nose?
Not for the squeamish of course, but I find videos/photos of people who survived head cancer or explosive/war injuries affecting that part of the face showing off their prosthetics to be the best visual examples of how big those nasal cavities are if they’ve been exposed.