I've been wondering about this. As far as I can tell, there is only a single reservoir. I've had the entire trunk disassembled, foung nothing. I've had most of the back seat area removed, found nothing. I highly doubt Toyota would hide a reservoir. What I did find is a platic tube under the long passenger kick plate that says "Celica" on it. It seems to be carrying liquid matching the same color as the washer fluid I insert in the engine bay. So that was when I gave up looking for it.
**NOTE - I did not disasseble all that stuff in order to look for the reservoir. I happened to be doing other work and looked around for it. Just thought I'd throw that in there.**