In order to get back into the beginning vent in the ceiling in the Facility level:
1. Stand on top of toilet in the stall directly under the hole in the ceiling.
2. Hold R and Right C
3. Hold Left on the control stick.
This should make you spin around counter clockwise on top of the toilet. After about one or two turns, you will suddenly launch into the vent. Make sure you quickly hit down on the control stick so that you back up into the vent and don't fall down again. This is useful in Multiplayer Mode.