I want to keep my Medela swing to use again if I have another baby, and I'd like your views on whether this would be safe. I know it's not a good idea to buy them second hand because they aren't a closed system so there's a risk of bacteria lurking, but I'm pretty sure that no milk ever got down the tube while I was pumping. Does this make it safe to use it again in future, or is it still a bit risky?