The important first step is preparation. You need to clean the pipes. There should be nothing left inside you before you commence on the trip. So take some laxatives and do some cleaning. After you’re thoroughly pristine you must only consume a clear liquid diet, so clear juices and soft drinks (make sure you consume the full sugar version because that’s how you’ll get your energy). Take a multivitamin each day. On the second or third day take an Imodium, this is likely overkill but you won’t poop. Return to a normal diet on the third day but do so gradually over the course of a day or two. I cannot guarantee that this method will not damage your health and the risk will likely be greater if you have other health conditions, but you wont poop sooo.