In this paper we discuss the most likely cause of most (but not all) occurrences of flare pulsation. The periodic surges of flame that occasionally burst forth from elevated flares into the quietude of the nighttime sky are often caused by seal drum sloshing. We explain how seal drum sloshing arises, how to tell if seal drum sloshing is the problem and what to do about it if it is. We show that the diagnosis, cause and elimination of flare pulsation due to seal drum sloshing is most easily understood in terms of The Fluid Mechanics of Beer Steins. The exact analytical solution is recounted briefly and several verifying experiments, including one you can do in a coffee cup or in a large mason jar, are suggested. Finally several real world examples that prove the theory are discussed.