I usually just use baby wipes or like those anti-bacterial wipes for hands, like Wet Ones I think the brand is. When I want to thoroughly wash them I use water and hand or dish soap. I don't think soap will cause the domes to crack, I never had a problem with that. Only time I've had cracked domes is one was shipped to me that way so I think it was probably mail handlers dropping the package, and like one of my large domes now is cracked because it fell. Never had a dome crack from pumping or anything like that.