I've used Preston in the past currently using Infinity Wax but use the same dilution.
I have a couple of old 5l containers with the pourer can't remember if they're Prestone but think they are.
In the winter I fill them half water half screenwash. So I've always got at least 10l of screenwash.
In the summer I actually dont use my washers much so tend to dilute it 2 parts water to 1 part screenwash which tends to get rid of bugs 👍🏼