The innuendo is much too easy.
That aside. Think of how hydraulics work. Since we are working with circles here.. the surface area is increases with radius at a rate of r squared. So say you have a 2 inch radius surface of exposed water in the base and 0.5 inch radius of exposed water in your stem itself.. If you were to add an additional 1 psi to the inside of the base, you would essentially be pushing 8 psi through the pipe. I know it's not quite that much in this case because of the surface area consumed by the pipe in the water in the base itself, but it's close enough. Either way, even if your purge is working, you can still do a "hookah volcano" as i read it if you do blow too hard.
I believe this can also be amplified by surging airflow into the hose for the purge. So even if the purge is working, and depending on the height of your hookah, and the resistance of the purge. you could have easily just blown too hard and unleashed a load (of water) all over your shisha.