Yes, it may not sound believable to most, but I know what you mean.
When I bought my car it came with a full windshield washer tank. It is still full, despite the fact I've never added any liquid in there. During the first few years of ownership the car was worked on a few times at BMW dealers and indys, so at some point somebody may have topped off the tank, I don't know for sure.
I won't bother to remove the tank, although replacing it with a smaller one that fits into the empty battery bay under the hood sounds like a good idea.