Abstract: A form assembly for use with a rough-in floor drain line, extending from a ground location prior to the pouring of a concrete aggregate. A body is constructed of a plasticized material and exhibits a three-dimensional outline with a height, width and depth and an open interior. The body further includes a bottom-most extending and encircling lip and an upper rim edge. The body is positioned so that the open interior surrounds the exposed floor drain line and a volume of a sand aggregate is filled into the open interior over and around the exposed drain. A lid is secured over the rim edge and a plurality of elongated and ground-securing stakes are engaged through apertures associated with the bottom extending said lip, in order to secure the body upon the ground location and to isolate the floor drain line from a volume of encircling and poured concrete.