“Some women experience sensual pleasure from pumping milk from their breasts or expressing milk manually—with or without a partner. In addition to the sensual pleasure, women have reported feeling more feminine while producing milk and continue with lactation for emotional or sensual reasons after weaning a baby.”

Source: Fiona Giles: Fresh Milk – The Secret Life of Breasts, NY: Simon and Schuster; Sydney: Allen and Unwin, 2003

See also:
Hospital grade breast pump
Breast pump