Abstract: The swimming pool floor or spa floor drain assembly includes a drain cover having an annular upper opening to serve as a fluid flow inlet, a fluid flow opening within a drain body below the mouth and a sidewall interconnecting the annular upper opening with the fluid flow opening. A support structure positions the plug within the drain body such that a substantial portion of the plug sidewall is spaced apart from the drain body sidewall to define a fluid flow channel having a first comparatively larger cross sectional area in proximity to the drain body mouth and a second comparatively smaller cross sectional area in proximity to the drain body outlet. The variation in cross sectional area from the drain body mouth to the drain body outlet provides a lower fluid flow velocity at the mouth than at the outlet when fluid is transferred through the floor drain assembly.