A camera down the throat is an endoscopy. A camera up the rear end is a colonoscopy.
Foods high in fibre such as Kelloggs' All - Bran, bamboo etc. may help in restoring a healthy gut, as does kimchi or sauerkraut.
Alternatively, a good cleanout can be achieved with PEG 3350, known under various names such as Macrogol, Moviprep, Glycoprep etc.
When doing a colonoscopy, the surgeon pumps up the colon with air, like a football. In rare cases, called barotrauma. too much pressure can cause injury.