Complex sentence: She filled her mouth with water before the séance started, but when the lights were turned off would swallow the water and before the end of the séance would refill her mouth with water from a corked test tube.
Split into simpler sentences: She filled her mouth with water before the séance had started, but when the lights were turned off would swallow the water. Before the end of the séance she would refill her mouth with water from a corked test tube.