[James98]

Trial and error. But you should not pump hard enough to experience any side effects. No red dots, no misting in the cup, no blisters or bruises. Apply a generous amount of lubricating oil like coconut oil or almond oil. Stop every 15 minutes to remove the cups and do a couple of minutes of massaging. You will find that over the weeks your skin with toughen up and then you can and should pump a little harder. Minimum of 1 hour a day, some get better results with up to 4 hours. But also take days off with just massage and no pumping.