Place a level on the floor surface to check if it's even. If it's not level, combine mortar mix with water, based on the product's package directions. Spread the mortar with a trowel evenly on the subfloor. Taper the mortar to about 1/4 inch thick around the floor drain and do not place the mortar more than 2 inches closer to the edge of the shower base or the floor drain.
Press the shower pan into the mortar. Place the level on top of the pan at the front, back, sides and middle. If all sides are not level, spread the mortar until it is level.
Place a piece of cardboard on the bottom of the pan to protect it from cuts or scratches while you install the drain. Cut a hole in the middle of the pan with a utility knife to allow access to the drain.
Lubricate the caulk seal gasket and drain pipe with liquid hand soap. Slide the gasket onto the drain pipe. Snap the strainer plate on top of the drain.
Allow the mortar to dry overnight before using the shower.