We are going to build a PVC pipe nipple watering system (we saw one here on BYC and now we can't get the idea out of our head!). We'll have a mounted water tank on the outside, and a PVC pipe running on the inside and into the run, with two nipples inside and three outside. I was just wondering how people keep them from freezing up in the winter (if they do). Or should I use a different watering system in the winter? Thanks for the help!