When do you drain down?

HerbieHymer

were getting our first frost of the winter now, I wondered if other motorhomers always drained all the water out of the tank and boiler when it drops below zero or do you wait till it's potentially llike -5 or more. A few people have told me that our Hymer
will be fine as they are often taken on skiing holidays abroad and well insulated when compared to British built ones. Anyway, I'm rambling - your general comments / experiences would be appreciated!