1995 Toyota Camry

Due to the age of this vehicle, I would immediately suspect the radiator cap. A faulty cap would allow coolant to pass straight to the overflow tank. As well, pressure check the system, the pressure testing device also has attachments that will allow you to check the cap. And, hopefully spot the leak.
At this point, just call the cap a "maintenance" item. The cap is designed to do two things, 1) allow the sytem to reach temperatures over the boiling point, (every pound of pressure raises the boiling point 2 1/2 deg. F.) This allows the engine to reach these temps. Without boiling over, and 2) the cap if working properly will allow coolant to return from the overflow back into the radiator.