Your colon (large intestine0 is only that 5 or so feet. Beyond the ileo-secal valve is the small intestine. The valve prevents the material that has passed into the colon from backing up and causing big problems. This valve only goes one way - that's why the colonic can't go in any farther. This is one reason it is important to drink plenty of water. It helps to wash the debris and toxins from cleansing the upper reaches of the digestive system. The salt water washes help get things down to where the colonic is effective. Look at this valve like the ones in your heart - they keep stuff going in the right direction. Generally we are designed to have material moving thru us in only one direction. Hope this helps.
Jay