My windscreen now has the correct mixture of additive thanks to snoogie. Must admit after looking at what it would take to drain my reservoir I'd thought I could just "guess" that it holds around 4Ltrs and work from there. Like what anchorman said, "All I do with mine is keep topping up with neat as the winter progresses until I’m convinced it is quite strong!"
Now, with what snoogie said I can do accurate "top ups". All I have to do is make a mixture of the correct blend (say a couple of litres) and use that when topping up is required.
( See anchorman, IF you'd asked the forum right from the start you too could have correct mixtures) Oh yes, there's a lot of good info in this forum Hah, hah.
And thanks anchorman for the windscreen washers.pdf