Yes, juice fasting cleans out the colon along with helping the rest of the body in many ways. I try to juice fast at least 2 times a year. 7 to 10 days is a good length of time for me, although I have fasted for longer and shorter periods of time.
parasites like to nest between the lining of the intestines and the coating of black rubbery junk that accumulates from eating an unhealthy diet. Getting that junk out is key to eliminating parasites.