For the first time yesterday, I "discovered" the radiator expansion tank and peered inside. It looked like it was empty. Is there some sort of mark that shows how full it should be ? And if I top it up is it ok to use normal tap water ? Or do I need to get a bottle of coolant from Toyota ?

I'm going to be getting my cambelt and water pump changed very soon, so all the coolant will be changed soon anyway.

From what i remember, there is a mark on the side as to how much you put in and if you getting the work done before it gets really cold, just use tap water.

Yeah its on the back you have to lean right over.