Do the bathrooms have showers? You get a pinhole camera, some transmit the video feed and others store the content on a memory card. If you store the video on a memory card than you need daily access to the camera to switch the card our with a blank card. If you transmit the video that you have to worry about someone else also receiving the video since anyone can get it if they are on the right channel. As for where to place the camera, vents are good, fire alarms are good, putting it in a stall is a little more of a challenge but you could drill a hole either in a wall or in a toilet paper dispenser for the camera.
Keep up posted on your progress.
