Best way to cleanse your digestive system?

Best not to. Your body has a natural mechanism for eliminating waste, and generally it is better to let it handle it. Cleansing usually involves ingesting or inserting various 'natural' toxins which serve only to upset your gut's normal homeostasis (=balanced environment). Occasionally the body needs help restoring itself back to balance, esp after antibiotics, so probiotics may help in this specific case.