Assemble the grass catcher if that hasn't been done. Place the grass catcher’s frame inside the bag, making sure the rigid part of the frame reaches the bottom of the bag.
Press the vinyl bindings around the outside of the bag’s opening. Soak the bindings in warm water for several minutes if they are too stiff to go on the bag.
Bend down and lift up the rear door flap. Slip the hooks on the grass catcher’s frame into the pivot pins on the rear door. Let go of the rear door.
Close the mulcher door, on the side of the mower, completely so that all discharge goes into the bag. Unhook the bag to use the mower as a mulching or side-discharge mower.