Anatomy lesson:
The "wall" many describe is often mistaken as a second sphincter, it is not. It is in fact the sigmoid bend, a right angle bend from the rectum into the sigmoid colon. This bend is held in place by a loop ligament that keeps the rectum vertical and prevents the large intestines from dropping out of place.
In order to get around that bend you need to have either a highly flexible toy, which as WildDog said will still take practice to find the direction and opening of that bend. Or the ligament that holds the bend needs to be loosed over time allowing the sigmoid to be easily straightened for a straight path towards the descending colon.