It's better to have a manual pump to empty the breast as much as possible. I find that the electrical pump cannot do the work that manual pump does. Even there are no milk coming out by using electrical pump, I can still feel that some glands are blocked and the manual pump can be used to unblock the glands. The lactactaion consultaion suggested me to find at least one time in a day (either morning or night) to clear the breast as much as possible. I think it helps preventing blockage and mastitis from happening.