Cut an access hole in the ceiling material directly underneath the shower drain pan. Allow enough access room to get your hands up in the ceiling to work with tools. Drywall is a common ceiling material that is cut with a utility knife or drywall saw.
Pop off the metal shower drain cover with a screwdriver. If the cover is held on with screws, remove them with a screwdriver.
Measure the PVC drain pipe 6 inches down from the solvent joint and cut the pipe to provide access to the drain. Use a PVC handsaw to cut the pipe.
Unscrew the shower drain body from the shower drain strainer body with a pair of slip-groove pliers. If the drain strainer body turns, have another person hold the strainer body with a second pair of slip-groove pliers.
Clean the fiberglass drain mounting area with a mild abrasive cleaner and sponge.
Apply a bead of 100 percent silicone caulk to the underside of the mounting lip. Place the shower drain strainer body into the fiberglass shower pan, applying slight downward pressure.
Apply a thin bead of silicone to the shower drain rubber gasket and slide it onto the drain strainer body.
Coat the threads of the shower drain strainer body with plumber's PTFE paste.
Screw the shower drain body onto the shower drain strainer body and tighten with a pair of slip-groove pliers. Have another person apply slight pressure to the top of the drain strainer body to prevent the strainer body from turning.
Prime and glue a 2-inch PVC coupling onto the shower drainage pipe; use PVC primer and PVC glue.
Measure the distance between the shower drain hub and the PVC coupling hub with a tape measure and cut a length of 2-inch PVC pipe with a PVC handsaw.
Prime and glue the PVC pipe, inserting the pipe into the shower drain hub first. Insert the other end of the pipe into the coupling. Allow the primer and glue to dry according to the manufacturer's drying times.
Pour water into the shower drain to fill the trap and check for leaks.