if its already frozen go over the length with a few kettles, but to avoid that, after filling turn off the the tap, remove hozelock fitting both ends and pick up and walk length of pipe, lifting and dropping pipe, this pushes water down the length, and you can see it pouring out, go back opposite way doing the same, and back once more, until its empty, this takes 3mins, rather than 15mins the kettle way.
also bring in all you can from the van, reels etc and make sure the pipes are drained in van!