Eating lesser than full stomach helps you regardless you are going to fast or not. Eating plant based diet also helps you before a long fast. If you really want to cleanse before a fast, drink nothing but freshly squeezed vegetable and fruit juices, consumed within 20 minutes after making it. Also intermittent fasting helps as well.
I am not sure about posting and long fasts. Posting should be used for encouragement, questions, for others to learn from and keep yourself in check.