Two easily missed things during winterizing.
Just a couple things for first time winterizing people. First, before pumping antifreeze use a 5 gallon bucket and empty anything remaining in waste tanks. This will allow a greater concentration of antifreeze at the waste valves. Second, after done running antifreeze through faucets, toilet, etc be sure to loosen low point drains enough to allow any water at the caps to be replaced with antifreeze. One other note if you move your camper after winterizing. Again drain waste tanks and FW tanks once you park. Those tanks could have had water that moves to the valves while transport. It could dilute antifreeze in the waste tanks and cause a freeze or move water in the FW drain and cause a freeze. I know this from experience. Had service done to my camper after winterizing one year. Water that was harmlessly sitting on the bottom of one of the grey tanks moved to the valve during transport. The next spring that valve had frozen. Thankfully it was only that one valve and not all 4.