Yeah, I filled up the radiator and took it for a quick drive, not very far at all. Came back, expansion tank level looks about the time. Will check it again tomorrow.
It's all fairly academic at this point as there's very likely a leak somewhere so it's going to the garage on monday, but will still be interesting to see just how quickly it's leaking. Apparently there are a couple of places where it can leak without pooling on the ground.