Additional Study Information: This research study is for children age 12 to 16. In this research study, we will evaluate the safety, effectiveness and tolerability of two different doses of a bowel cleansing medication referred to as BLI-800. One group of study participants will receive the larger dose (6 oz.), which dose has been approved by the FDA for use by adults. A second group of study participants will receive the smaller dose (4.5 oz.). Finally, the third group of participants will receive a bowel cleansing medication called NuLYTELY that has already been approved by the FDA for use by children.