Complex sentence: The upper vat, know as the "steeper vat", was used for the fermentation of indigo plants with the liquor drawn through a small portal into the "beater vat" below.
Split into simpler sentences: The upper vat, know as the "steeper vat", was used for the fermentation of indigo plants. The liquor produced by this process was drawn from the "steeper vat" through a small portal into the "beater vat" below.