A discharge gate for a gypsum slurry mixer is provided, and includes a gate adapter having an inlet opening configured for receiving the slurry, and an outlet opening configured for delivering the slurry to a dispensing device. The gate adapter has two different transitioning cross-sectional geometries at opposite ends. Specifically, the gate adapter includes an inlet section having a quadrilateral inlet opening; an outlet section having a substantially circular outlet opening; and a transition section sandwiched between the inlet and outlet sections.